Mail Servers

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Two types of mail servers and protocols are used to process email:

• mail transfer
• mailbox access protocols:

• Internet email addresses follow the mailto URL scheme
  • comprises two parts
    • the username (local part)
    • the domain name, separated by an @ symbol
  • domain name may refer to a company or an ISP

The Simple Mail Transfer Protocol (SMTP) specifies how email is delivered from one mail domain to another.

• SMTP server of the sender discovers the IP address of the recipient SMTP server by using the domain name part of the recipient’s email address
• SMTP servers for the domain are registered in DNS using Mail Exchange (MX) and host (A/AAAA) records
• SMTP configurations use the following ports and secure services:
  • Port TCP/25
    • used for message relay between SMTP servers, or message transfer agents (MTAs)
    • usually unsecure
  • Port TCP/587
    • used by mail clients—message submission agents (MSAs)—to submit messages for delivery by an SMTP server
    • Servers configured to support port 587 should use encryption and authentication to protect the service