If you want to do something special after authentication, but before beginning the IMAP or POP3 session, you can do this by changing the mail_executable setting to run a script. Below are some examples for what this can be used for.
WARNING: The process still runs as root at this point! The privileges are dropped only after the imap process starts. You can change this by setting mail_drop_priv_before_exec=yes.
Standard input and output file descriptors are redirected to the client's network socket, so you can send data to client by simply writing to stdout. Standard error fd is redirected to Dovecot's error log, you can write errors there as well.
All of Dovecot's settings are passed via environment variables from master process to mail processes. Usually the settings have same names as in dovecot.conf, except uppercased. So for example mmap_disable setting shows up in MMAP_DISABLE environment variable. You can override any settings you want by modifying the environment before executing the imap/pop3 binary.
Note that boolean settings are enabled simply by having the environment variable exist. So MMAP_DISABLE=1 and MMAP_DISABLE=0 (and =anything) means the same as mmap_disable=yes.
The only list for mapping settings to environment variables exists in the source code (src/master/mail-process.c. Another somewhat easy way would be for you to get a list of all environment variables and find the settings you want to override from it:
#!/bin/sh set > /tmp/dovecot-environment exec /usr/local/libexec/dovecot/imap "$@"
The USER and IP environment variables come from the login process and are guaranteed to be sanitized.
If you want to know when the user last logged in, you can do it like this:
#!/bin/sh # a) Filesystem based timestamp in user's home directory touch ~/.last_login # b) SQL based tracking. Beware of potential SQL injection holes if you allow # users to have ' characters in usernames. #echo "update last_login = now WHERE user = '$USER'" | mysql mails # Finally execute the imap/pop3 binary. If you use both, you'll need two scripts. exec /usr/local/libexec/dovecot/imap "$@"
Note: if creating a timestamp inside the Maildir itself, it's better to avoid filenames which begin with a dot. The IMAP "list" command will show such files as IMAP folders, unless you also set maildir_stat_dirs = yes which generates more I/O ops.
Custom mailbox location autodetection
See MailLocation for an example.
If you want to give the user's client some warning notification, you can do it just by writing it to stdout. But note:
- Not all clients show the alerts, even though IMAP RFC requires it.
- IMAP protocol requires CRLF (\r\n) line feeds. Some clients will break if you only send LF.
- Don't write anything if user is "dump-capability", otherwise Dovecot uses your string as IMAP CAPABILITY string, which probably breaks all clients.
#!/bin/sh if [ -f ~/.out-of-office ]; then if [ "$USER" != "dump-capability" ] then printf "* OK [ALERT] You're still marked as being out of office.\r\n" fi fi # Finally execute the imap/pop3 binary. If you use both, you'll need two scripts. exec /usr/local/libexec/dovecot/imap "$@"
Use UNIX groups for ACL authorization
#!/bin/sh ACL_GROUPS=`groups $USER | tr ' ' ','` export ACL_GROUPS exec /usr/lib/dovecot/imap "$@"
Denying connection from some IP/User
You can use the IP and USER shell variables that are setup by dovecot in a bash script in order to deny connection (after a successfull login), like this:
if [ "$USER" = "myuser" ] ; then printf "* NO [ALERT] The user '$USER' can not login\r\n" exit 1 fi if [ ! "$IP" = "192.168.1.1" ] ; then printf "* NO [ALERT] Access not allowed from the Internet\r\n" exit 1 fi
Or use the Connect ACL Script for limiting some user from connecting from the Internet. More info here: http://www.linux.org.py/wiki/howto/dovecot_connect_acl