/usr/local/bin$ ls -l postlogin.sh
-rwxr-x--- 1 vmail vmail 401 May 11 19:50 postlogin.sh
/usr/local/bin$ sudo cat postlogin.sh
#!/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. Following is just an example:
echo "UPDATE mailbox SET lastlogindate=now(),lastloginipv4='$IP' WHERE username = '$USER'" | mysql vmail -uvmailadmin -pvmailadminpassword
exec "$@"

...
service lmtp {
  unix_listener lmtp {
    #mode = 0666
  }

  # Create inet listener only if you can't use the above UNIX socket
  #inet_listener lmtp {
    # Avoid making LMTP visible for the entire internet
    #address =
    #port =
  #}
  executable = lmtp custom-postlogin
}

service imap {
  # Most of the memory goes to mmap()ing files. You may need to increase this
  # limit if you have huge mailboxes.
  #vsz_limit = $default_vsz_limit

  # Max. number of IMAP processes (connections)
  #process_limit = 1024
  executable = imap custom-postlogin
}

service pop3 {
  # Max. number of POP3 processes (connections)
  #process_limit = 1024
  executable = pop3 custom-postlogin
}

service custom-postlogin {
  # all post-login scripts are executed via script-login binary
  executable = script-login /usr/local/bin/postlogin.sh

  # the script process runs as the user specified here (v2.0.14+):
  user = vmail
  # this UNIX socket listener must use the same name as given to imap executable
  unix_listener custom-postlogin {
  }
}

...