Global options

listen-address: address[:port][(domain)|/regex/][;tls-options] ...

Specify an address and optional port on which incoming connections are accepted. domain is the domain name for which the service is operated; alternatively, if mass virtual hosting support is compiled in (the default), then you can specify regex, a POSIX extended regular expression containing a single bracketed subexpression, instead of domain; in this case, the regular expression is applied (in a case-insensitive sense) to the name of the host to which the client has connected, and the matching subexpression is used as the domain name. This only really makes sense if address is 0.0.0.0 (INADDR_ANY). If neither domain nor regex are given, the portion of the name associated with the given address following the first `.' is used, or, if no such name can be established, the nodename of the system determined by uname(2). If any port is not specified, it is assumed to be 110 (pop-3), or 995 (pop-3s) if in `immediate' TLS mode.

If tpop3d has been compiled with support for TLS (`SSL'), then you may specify additional tls-options for each address, in the following form:

  tls=(immediate|stls),certificate[,private-key]
    

The first token after tls= specifies the mode of TLS operation in use on this address. There are two widely-supported modes of POP-3-over-TLS operation. In the first case, which we call immediate mode, TLS negotiation is initiated immediately after a connection is received. In this mode, only TLS connections can be made to a particular address. In the other mode, the client establishes an unencrypted TCP connection, then issues the POP-3 command STLS to initiate TLS negotiation. We call this stls mode. This mode permits unencrypted and TLS operation on the same address.

The cryptographic identity to use for this address is read from the files named by certificate and private-key. If only certificate is given, then both the certificate and the private key should be contained in the one file. If a pass-phrase is required to make use of the certificate or private key, then tpop3d must be started with the -P option (see tpop3d(8)) to read the pass phrase from the terminal.

To listen for connections on any interface and the default port, the directive

  listen-address: 0.0.0.0
    

is sufficient. To specify a specific domain, use this syntax:

  listen-address: 12.34.56.78(example.com) 0.0.0.0(example.org)
    

If, alternatively, the machine has numerous interfaces with names pop3.example.com, pop3.example.org, etc., you could specify

  listen-address: 0.0.0.0/^pop3\.(.*)$/
    

to accept incoming connections and associate them with the proper domains. Note that for this to work, all interfaces on which connections are to be accepted must have functioning inverse name resolution; also, in this case, tpop3d will do a name lookup for each incoming connection, which may block in the event of a DNS failure. You may wish to create some other mapping -- perhaps in /etc/hosts -- to ensure that this does not occur.

max-children: number

The maximum number of child processes which may be actively serving connections at any given time. Consists of a single number. By default, this is set to 100.

append-domain: (yes|true)

If authentication does not succeed for a given username, retry with username@domain, where domain is the domain name associated with the address on which the connection was received. This is intended to be used where multiple virtual domains are served from multiple IP addresses. This option only takes effect when username does not contain a separator. See below for a more detailed description.

strip-domain: (yes|true)

If authentication does not succeed for a given username, and the username supplied is in the form username@domain, try the authentication again with a bare username. domain need not be the domain name associated with the address on which the connection was received. This is intended to be used where multiple domains are served by a single authenticator with the same username, such as when username@domain.com and username@domain.net are equivalent and served from the same machine. This option only takes effect when username contains a separator, which may be specified via the domain-separators config option. (see below)

domain-separators: string

Specify which characters may be used to separate local_parts from domains in POP3 usernames. The default is "@%!:".

apop-only: (yes|true)

Disconnect any client which attempts plaintext USER/PASS authentication. The intention of this option is to discourage users from sending plaintext passwords over the network, so it has no effect when a user is connected over a TLS-secured connection.

lowercase-user: (yes|true)

Convert the string provided with the POP3 USER command to lowercase letters. This may be usefull with case-sensitive operations like authentication against dbm files or case-sensitive SQL databases.

timeout-seconds: number

This is the number of seconds for which a connection may be idle for before it is closed. If it is set to 0, then timeouts are disabled. The default value is 30 seconds (see the section on BUGS in tpop3d(8)). If you wish to have tpop3d comply explicitly with the RFC (which demands a ten-minute timeout), then specify 600 seconds. This may be necessary with some clients which pause randomly whilst downloading messages.

tcp-send-buffer: number

This is the largest number of bytes which may be `in flight' between the server and a client at any time. Setting this to larger values may improve the performance of tpop3d, but at the risk of timing out clients connected by slow networks. You should not set this parameter to anything larger than the timeout multiplied by the data rate (in bytes per second) of the slowest network through which clients will connect to the POP3 server. This is set using the SO_SNDBUF socket option; see socket(7) for more information. The default is 16,384 bytes; set this to 0 to use the system default.

log-facility: facility

This selects the `facility' as which tpop3d emits system log messages. Possible values for facility are: mail, authpriv, daemon, user, and local0 through local7 inclusive. (Although other possibilities are mentioned in openlog(3), they don't make much sense for a POP3 server.)

log-level: level

This selects the `level' at which tpop3d logs system log messages. Possible values for level are described in syslog.conf(5).

log-stderr: (yes|true)

Send log messages to standard error as well as the system log. This makes sense only when tpop3d is running with a controlling terminal.

no-detach: (yes|true)

Do not detach from controlling terminal. The -d command-line option to tpop3d is equivalent to combining this and the log-stderr directives.

mailbox: [mailbox-driver:]path-spec ...

This selects the location, and optionally the type, of the mailbox to use when a user is authenticated. Mailbox-driver should be one of the names listed when you execute tpop3d -h; if left blank the default (first available) one is used, but this is discouraged as it may vary between builds of tpop3d. Path-spec should give a path name in the file system; you can use the substitution strings $(user), the username supplied to the POP server by the client; $(local_part), the local part of a client's email address in a virtual-domain authentication, $(domain), the domain, and $(home) for the user's home directory. In addition, the syntax $(foo[index]) may be used to select a given letter of the string. 0 is the first character, and -1 the last. This allows the used of `hashed' spool directories; for example,

  mailbox: bsd:/var/spool/mail/$(user[0])/$(user)
    

If several mailbox locations and types are specified, tpop3d will try each in turn, stopping when it opens a mailbox or encounters an error other than the mailbox not being present. This means that if your users have both maildir and bsd mailboxes, you can use something like

  mailbox: maildir:$(home)/Maildir bsd:/var/spool/mail/$(user)
    

to support both.

Some authentication drivers will set the mailbox explicitly, overriding this option. Those that do not also have a specific option, of the form auth-foo-mailbox: which overrides the global setting.

lowercase-mailbox: (yes|true)

Convert the directory/file part of the mailbox specification (see above) to lowercase letters, if retrieved by an authentication driver. (E.g. due to a database lookup.) Usefull only in cases where case-sensitive filesystems are in use, of course.

mailspool-index: path-spec

This selects the location of metadata cache files for BSD mailspools, based on their file names. This option is only available when tpop3d is compiled with metadata caching enabled, and it is only switched on when this option is specified.

Path-spec gives the location of the metadata cache file, using substitution strings similar to those for the mailbox option above. In particular, you can use $(name), the full name of the mailspool; $(path), the directory containing the mailspool; $(file), the file name of the mailspool (the part after the final `/'); and $(escaped_name), which is the full name of the mailspool escaped using the HTTP-style %.. convention so that it does not contain any slashes.

Examples include:

  mailspool-index: $(name).tpop3d-index
  mailspool-index: /var/spool/tpop3d/$(escaped_name)
    

In order to use this facility, tpop3d must be able to write the metadata cache files to the locations specified. If you choose to use a specific directory for this (for instance, /var/spool/mail or /var/spool/tpop3d), you will need to set appropriate permissions. 1777 (as for /tmp) is probably the best choice. tpop3d will overwrite any file whose name is the same as the specified cache file for a given mailspool; therefore, it is recommended that the mailspool index files be stored in a directory to which users would not customarily have access, for instance /var/spool/tpop3d.

mailspool-no-dotfile-locking: (yes|true)

By default tpop3d will try to lock a mailspool for exclusive access using all methods available on the local system: fcntl(2), flock(2), and creating a lockfile for the mailspool with a `.lock' suffix. This option allows you to switch off the last of these without recompiling the daemon, and is recommended if you are absolutely certain that no other programs rely on dotfile-locking to synchronise access to mailspools. In particular, if you use lockfiles, it is possible for an over-quota user to be unable to log in to the POP3 server, because creation of the lockfile is prohibited; switching on this option eliminates that possibility.

maildir-exclusive-lock: (yes|true)

Indicates that tpop3d should attempt to lock maildir mailboxes for exclusive access, so that it more closely follows the behaviour described in RFC1939. Even if not specified, tpop3d behaves intelligently when a message in a maildir is moved or deleted, so this option is not necessary.

maildir-recursion: (yes|true)

Tells tpop3d to display messages in IMAP folders as if they were in the INBOX. Useful if you mix POP3 with IMAP clients such as webmail systems.

maildir-ignore-folders: [foldername [...]]

Specifies IMAP folders (without the leading dot) that should be excluded from maildir-recursion. May be empty; more than one folder should be separated by spaces or tabs. Items beginning with "^" are treated as POSIX Extended Regular Expressions.

The default is:

  maildir-ignore-folders: Trash Sent
    

maildir-evaluate-filename: (yes|true)

If enabled, tpop3d tries to extract information about modification time and message size out of the message filenames when reading a maildir. This saves some disk I/O, as we don't have to stat() on each file. Extraction of information from the unique filenames in a maildir is NOT common practise, so use with care! You have to ensure, that message filenames conform to the following pattern:

The message filename has to begin with the UNIX timestamp of the time the message was delivered. The size of the message in bytes may appear anywhere in the filename but has to be preceded with a unique string, which can be altered by maildir-size-string in tpop3d.conf.

If a message filename does not conform correctly, tpop3d may misinterprete what it found, allthough if the filename turns out to be definately unusable (e.g. the unique string is not found, or it doesn't start with digits) it will fall back on using stat().

Message filenames are by default set correct by reasonable recent versions of qmail-ldap, exim users may use the maildir_tag option of the appendfile transport to conform.

maildir-size-string: string

Specifies the unique string tpop3d will search for when evaluating message filenames to find the messages size. See maildir-evaluate-filename for information on how this is used.

The default is:

  maildir-size-string: ,S=
    

uidl-style: stylename

The UIDL command is used by POP3 clients to distinguish messages they allready downloaded from new ones. If you switch between POP3 server software that produce different unique-ids, these clients will download all messages again. To avoid this, tpop3d supports different unique-id formats.

The available formats are: tpop3d: tpop3ds native format, the default and fallback. qmail: qmail-pop3ds format, uses message-filenames as unique-ids.

tcp-wrappers-name: name

This selects the `daemon name' used by tpop3d when it tests connections against the TCP Wrappers access-control-mechanism. This corresponds to the part of an entry before the first colon in hosts.allow or hosts.deny. If not specified, this will default to `tpop3d'. This feature is only available if tpop3d has been compiled with support for TCP Wrappers.

drac-server: hostname

If specified, gives the name of a server to which tpop3d should send DRAC notifications about successful logins.

whoson-enable: (yes|true)

Enable notification of successful logins to a WHOSON server as defined in /etc/whoson.conf.

tls-no-bug-workarounds: (yes|true)

Disable workarounds for various bugs in client TLS implementations, as described in SSL_ctx_set_options(3). Only available if tpop3d has been built with TLS support.

Options relating to authentication

Authentication is supported using the conventional USER/PASS method, or the challenge-response APOP method. When a client connects to tpop3d and attempts authentication, a request is passed to each of a number of configured authenticators in turn, until the client is successfully authenticated or all authenticators have been tried.

The information supplied with each request consists of user, the user name as supplied by the client; local-part, the local-part of a virtual-domain email address, and domain, the domain in which authentication is taking place. By default, domain is the domain associated with the address to which the client has connected.

If the client's supplied username contains one of the characters `@', `%', `:' or `!', it is interpreted as a local-part@domain combination, and the given local-part is used while the given domain replaces the domain derived from the address to which the client connected.

If there is no separator, authentication is first attempted with no local-part and the default domain; if this does not succeed, and the append-domain global option is set, then authentication will also be attempted with the local-part the same as the supplied user and the default domain.

For example, if the client sends the command

  USER foo

  user       = foo
  local-part   not set
  domain     = dom

  user       = foo
  local-part = foo
  domain     = dom

If instead the client says:

  USER foo@bar

  user       = foo@bar
  local-part = foo
  domain     = bar

These global options apply to all authenticators:

permit-empty-password: (yes|true)

If enabled, users may log in with an empty password. (Note that their client must send a space after the PASS command in this case.)

onlogin-child-wait: (yes|true)

If enabled, and the authenticator offers an `onlogin' action to be taken when a user logs in, the user's mailbox won't be opened until after the onlogin action completes (otherwise, the child does not block in this way). This is intended to allow you to use the onlogin feature to implement server bulletins and similar features.

log-bad-passwords: (yes|true)

Log incorrect passwords supplied by users who fail to log in. Use of this option is an invasion of privacy, but may be useful for debugging client configuration problems.

no-commit-on-early-close: (yes|true)

Some POP3 clients (most notably Microsoft `Outlook') will close their connection to the server immediately after issuing a QUIT command and before receiving any response. Strictly they oughtn't to do that, and historically if they did, tpop3d would abort the connection and not delete messages for which DELE commands had been issued during the session. That behaviour has been changed for greater compatibility with broken clients; you can set this option to restore the previous behaviour. Doing so will reduce the chance that your clients will lose mail due to flakey network connectivity.

tpop3d can cache the results of successful login attempts, and re-use them when the same user logs in again. This is probably not useful except for servers which run under very heavy load. Authentication cacheing can only be used for USER/PASS authentication; it has no effect on APOP authentications. The following options control the authentication cache:

authcache-enable: (yes|true)

Enable the cache. It is off by default.

authcache-entry-lifetime: number

The number of seconds for which the results of a successful authentication are cached. The default value is 1 hour (3600 seconds). In order to be useful, this value must be much larger than the mean interval between POP sessions by a given client. For instance, if clients check mail every five minutes, then setting the lifetime to ten minutes will mean that, on average, half of authentications come from the cache and are fast. Setting it to one hour means that eleven out of twelve authentications come from the cache, and so forth. But note that this value also controls how long it takes for password changes to take effect!

authcache-use-client-host: (yes|true)

Some authenticators allow you to control authentication based on the IP address of the connected client. By default, the authentication cache ignores this information, so that a client which connects from more than one IP address (for instance, if their DHCP lease changes) can still be authenticated from the cache. But if you have authenticators whose behaviour varies based on client IP address, you must switch this option on, since otherwise the cache will give incorrect results in some cases.

PAM authentication options

auth-pam-enable: (yes|true)

Enable authentication using Pluggable Authentication Modules.

auth-pam-facility: facility

Sets the PAM facility name used by tpop3d to facility. Defaults to tpop3d.

auth-pam-mail-group: (group-name | gid)

The group name or gid under which access to the mailspool will take place. The default for this option is the primary group of the authenticated user, which may not work. You will normally want to set this to `mail'.

auth-pam-mail-user: (user-name | uid)

In normal operation, auth-pam will only authenticate users who have local accounts (i.e., for whom there exists a passwd entry and a distinct user ID). It is also possible to use PAM to authenticate arbitrary user names. This option names a local user whose credentials are used for users without local accounts who are authenticated by PAM. This option will not be useful in a typical configuration.

Password authentication options

auth-passwd-enable: (yes|true)

Enable authentication using /etc/passwd.

auth-passwd-mail-group: (group-name | gid)

The group name or gid under which access to the mailspool will take place. The default for this option is the primary group of the authenticated user, which will probably not work. You will normally want to set this to `mail'.

MySQL authentication options

auth-mysql-enable: (yes | true)

Enable MySQL authentication.

auth-mysql-mail-group: (group-name | gid)

The group name or gid under which access to the mailspool will take place. The default for this option is the primary group of the UNIX user associated with the virtual domain.

auth-mysql-hostname: hostname

Host on which to connect to MySQL, by default localhost. You may specify several hosts, separated by spaces or tabs. These hosts are tried in order until one is found working. The same database name, username and password are tried on each host.

auth-mysql-database: database

MySQL database to use for authentication.

auth-mysql-username: username

MySQL username used to access the database.

auth-mysql-password: password

Password of MySQL user.

auth-mysql-pass-query: substitution string

Query template to use for USER/PASS authentication.

auth-mysql-apop-query: substitution string

Query template to use for APOP authentication.

auth-mysql-onlogin-query: substitution string

Query template to use for POP-before-SMTP operation.

Since mailbox names are stored in the database, the auth-mysql-mailbox: setting is ignored.

A note on MySQL authentication

However, it is also possible to use the auth-mysql-pass-query and auth-mysql-apop-query directives to specify the SQL syntax for a query to use against any database schema. These should specify queries which return the mailbox file location, password hash, Unix user and mailbox type, in that order. The variables $(user), $(local_part) and $(domain) are escaped and substituted into the string, in the same way as for the mailbox path specifications described above. In addition, the numerical IP address to which the client connected is substituted for $(serverhost).

The nature of password hashes is described more fully in README.auth_mysql in the distribution. If you do not wish to use either of USER/PASS or APOP authentication, specify the value none for the relevant configuration directive; otherwise, the default (vmail-sql) query will be used.

As an example, if you have a table called users which contains fields login, domain, cryptpw and the Maildir mailboxes for the users are under /path/to/$(domain)/$(local_part), then you could use

  auth-mysql-pass-query:                      \
      SELECT CONCAT('/path/to/', '$(domain)', \
                    '/', '$(local_part)'),    \
             CONCAT('{crypt}', cryptpw),      \
             'mail', 'maildir'                \
        FROM users                            \
       WHERE login = '$(local_part)'          \
         AND domain = '$(domain)'

The auth-mysql-onlogin-query specifies an SQL statement (most likely an INSERT or UPDATE) which is executed after a successful login. This is intended to allow you to insert a record into a database table used to permit relaying in a `POP-before-SMTP' scheme. For this query, the additional value $(clienthost) indicates the connected client host, as a numeric IP address. This statement will be executed for any successful login, not only auth-mysql logins. Note that $(local_part) may not be supplied for a given login, so you should only use it if you are sure that all relevant logins will specify it. See the description of authentication, above, for more information. If more flexibility is required, consider using auth-other or auth-perl instead.

Note that the username and password supplied in the configuration file are privileged information, in the sense that they would allow an arbitrary person to obtain information from the database if they have access to the machine on which it resides. The corollary to this is that the tpop3d.conf file should not be readable by arbitrary users.

Postgres authentication options

auth-pgsql-enable: (yes | true)

Enable Postgres authentication.

auth-pgsql-username

auth-pgsql-password

auth-pgsql-database

auth-pgsql-hostname

auth-pgsql-pass-query

auth-pgsql-apop-query

auth-pgsql-onlogin-query

auth-pgsql-mail-group

Behave like the equivalent auth-mysql options.

LDAP authentication options

auth-ldap-enable: (yes | true)

Enable LDAP authentication.

auth-ldap-url: substitution string

Template giving an LDAP URL indicating the server against which to make authentication requests. Note that the variables $(user), $(local_part) and $(domain) may appear only in the DN part of the URL.

auth-ldap-tls: (yes | true)

Use an encrypted connection to contact the LDAP server.

auth-ldap-searchdn: LDAP server username

DN to use when binding to LDAP server to search for a user.

auth-ldap-password: LDAP server password

Password of search user.

auth-ldap-filter: substitution string

Filter template to use when searching for a user's account.

auth-ldap-scope: (subtree|base|onelevel)

Scope of LDAP searches. If not specified, the default is `subtree'.

auth-ldap-mailbox: [mailbox-driver:]path-spec ...

User mailbox location, as described above.

or

auth-ldap-mailbox-attr: attribute name

auth-ldap-mboxtype-attr: attribute name

LDAP attributes which contains the name of a user's mailbox, and its type. If the type is not specified, or if the attribute is not present for a given user, the driver will guess that mailbox names which end `/' are of type maildir, otherwise of type bsd.

auth-ldap-mail-user: (user-name | uid)

auth-ldap-mail-group: (group-name | gid)

User and group under which access to the mailbox will take place.

or

auth-ldap-mail-user-attr: attribute name

auth-ldap-mail-group-attr: attribute name

LDAP attributes which specify the user and group under which access to the mailbox will take place.

A note on LDAP authentication

Information about the user's account, in particular, the user and group id to use for mailbox access, and the location and type of the mailbox, may be obtained either from the directory, or from values in the configuration file.

Flat file authentication options

auth-flatfile-enable: (yes | true)

Enable flat file authentication.

auth-flatfile-passwd-file: substitution string

Specify the file in which tpop3d will search for a user's password.

auth-flatfile-mail-user: (user-name | uid)

auth-flatfile-mail-group: (group-name | gid)

User and group under which access to the mailbox will take place.

A note on flat file authentication

External program (`other') authentication options

auth-other-enable: (yes | true)

Enable external program authentication.

auth-other-program: path

Program to use for external authentication; this must be an absolute path and should process requests as described below.

auth-other-user: (user-name | uid)

auth-other-group: (group-name | gid)

The user and group under which to run the authentication program.

auth-other-timeout: time

The timeout in seconds for authentication; may be a fractional value, by default 0.75.

A note on external program authentication

An external authentication program reads data `packets' structured in the following format on its standard input:

  key\0value\0 ... \0

Defined keys are:

method = (APOP | PASS)

Authentication mechanism being attempted.

user = username

The username being sent with an APOP or USER command.

local_part = local-part

(Sent only for virtual-domain authentication.) The local-part of the client's email address.

domain = domain

(Sent only for virtual-domain authentication.) The domain of the client's email address.

clienthost = IP number

The host from which the client is connected to the POP server.

serverhost = IP number

The address to which the client connected on the POP server.

timestamp = timestamp string

(APOP only.) The `timestamp' string sent by the server to this client.

digest = hex digest

(APOP only.) Hex representation of the MD5 digest sent by the client with an APOP command.

pass = password

(PASS only.) The password sent with a PASS command.

In response to an APOP or PASS request, the program should write to standard output `packets' in the format described above. Defined keys are:

result = (YES | NO)

Was authentication successful?

logmsg = string

(Optional.) Specifies a message to be written to the system log.

The following apply only if authentication is successful; all but uid and gid are optional:

uid = (user-name | uid)

gid = (group-name | gid)

The user and group with which to access the mailspool. Note that the user must have a valid home directory.

domain = domain

The domain in which the user has been authenticated.

mailbox = path

Path of this user's mailbox.

mboxtype = mailbox driver

The type of the mailbox.

If the mailbox is not specified, then the normal mechanism (via configuration directives mailbox: and auth-other-mailbox:) is used.

Your authentication program will also receive packets describing any successful login. These may be used to implement POP-before-SMTP relaying. Such packets have the form

method = ONLOGIN

Indicating that the packet describes a login.

user = username

The username as supplied by the client.

local_part = local-part

domain = domain

The local-part and domain of the authenticated user.

clienthost = IP number

The host from which the client is connected to the POP server.

The only valid responses to an ONLOGIN request are an empty packet or one containing only a logmsg directive.

Note that tpop3d requires external authentication programs to respond in a timely fashion, since authentication blocks the main daemon; if no response is received within the timeout period specified, then the program will be killed with SIGTERM; if it fails to expire, SIGKILL will then be sent. An authentication program should catch SIGTERM to do any essential cleaning up.

Your authentication program must not leak memory or file descriptors; if this is a problem, have it exit after some number of transactions; tpop3d will restart it automatically.

Perl authentication options

auth-perl-enable: (yes | true)

Enable authentication via an embedded perl interpreter.

auth-perl-start: perl code

Specify a line of perl code to be executed at startup; in most cases, this should be something like

  auth-perl-start: do '/usr/local/etc/tpop3d/tpop3d.pl';
    

auth-perl-finish: perl code

Specify a line of perl code to be executed when the authentication driver is shut down.

auth-perl-apop: subroutine name

Specify the name of a perl subroutine which will be called when a request for APOP authentication is received.

auth-perl-pass: subroutine name

Specify the name of a perl subroutine which will be called when a request for USER/PASS authentication is received.

auth-perl-onlogin: subroutine name

Specify the name of a perl subroutine which will be called after a successful login for POP-before-SMTP operation.

A note on perl authentication

Your perl routines must not leak memory (normally not a problem because of perl's garbage collector) or other system resources. If this is a problem, you could consider forcing tpop3d to restart every so often by calling kill(1, $$), but it would probably be preferable to use auth-other in this case.

GNU dbm authentication options

auth-gdbm-enable: (yes | true)

Enable authentication via a GNU dbm file.

auth-gdbm-passwd-file: string

Specify the dbm file in which tpop3d will search for a user's password.

auth-gdbm-persistent: (yes | true)

Tells whether tpop3d should keep the GDBM file open (persistent: yes) all the time, or whether it should be reopened for each authentication request. The former should give slight better performance on heavy loaded servers, the latter is easier to handle. If you use persistent filehandles, you'll have to send a HUP signal to the listener process every time after replacing the GDBM file.

auth-gdbm-mail-user: (user-name | uid)

auth-gdbm-mail-group: (group-name | gid)

User and group under which access to the mailbox will take place.

A note on GNU dbm authentication