Mail system architecture
| Agent | Role | Example |
|---|---|---|
| MUA / UA | Read and compose mail | Thunderbird, mutt |
| MSA (optional) | Accepts outgoing mail from MUA, grooms it, submits to transport | Postfix submission (port 587) |
| MTA | Routes messages among machines | Postfix, Exim, Sendmail |
| DA | Places messages in local message store (mailbox or database) | procmail, Dovecot LDA |
| AA (optional) | Connects user agent to the message store | Dovecot (IMAP/POP) |