Is it necessary to use the 'citmail' MDA?

No. For the vast majority of installations, citmail is completely unnecessary.

The Best Option: Let Citadel Be Your MTA and MDA

The simplest, fastest, and most reliable configuration is to let Citadel handle both roles directly:

• Mail Transfer Agent (MTA): Citadel listens directly on port 25 for incoming SMTP connections and handles outbound delivery to remote hosts.
• Mail Delivery Agent (MDA): Citadel deposits messages directly into user mailboxes and rooms in the database.

If Citadel is the primary mail system on your server, simply disable any other mail transfer software (such as Postfix or Exim) and let Citadel manage port 25. This eliminates intermediate spooling, duplicate queues, and unnecessary configuration complexity.

Handling Special Circumstances

If you have unique architectural requirements where an external service must listen on port 25 (for example, a specialized mail filtering gateway or custom routing system), Citadel offers two ways to receive delivered mail:

• Direct LMTP Socket (Preferred): Modern MTAs support LMTP (Local Mail Transfer Protocol). You can configure your front-end mail server to deliver incoming messages directly to Citadel's UNIX domain socket, lmtp.socket, located in Citadel's runtime directory.
• The citmail Utility: If you are working with an external script or legacy mail program that can only pipe messages to an executable, the citmail binary serves as an MDA bridge. It receives a message on standard input and injects it into Citadel using LMTP.