Mail Notes

1. Definitions

MUAs

Mail User Agents, let a user read, compose, and send email. Mail Clients like Apple Mail, Thunderbird, and Outlook are MUAs.

MTAs

Mail Transfer Agents, handle the transport, delivery, and forwarding of email. SMTP servers like Exim, Postfix, and Qmail are MTAs

SMTP Relayer

Because of rampant SPAM, residential ISPs are no longer trusted to send mail and thus are blocked.
In order to send email from your local email server using a residential ISP to an external mail server, you’ll need to use a trusted 3rd party SMTP Mail Relayer service.

2. Mail Component Diagram

  • The following diagram depicts mail server related components and ports.

    Expand for Mail Component Diagram
    mail-relayer
    Figure 1. Mail Component Diagram

3. Router Port List

  • Configure your router to forward the following ports to your mail server’s local IP address.

    Expand for Port list
    Port Name Notes

    25

    SMTP - mostly processing incoming mails from remote mail servers

    110

    POP3 - standard protocol for accessing mailbox, STARTTLS is required before client auth

    143

    IMAP - standard protocol for accessing mailbox, STARTTLS is required before client auth

    465

    SMTPS - Legacy SMTPs port

    587

    MSA - SMTP port primarily used by email clients after STARTTLS and auth

    Use this instead of port 25

    993

    IMAPS - alternative port for IMAP with encryption from the start of the connection

    995

    POP3S - POP3 port with encryption from the start of the connection

    4190

    Sieve - remote sieve settings