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SMTP Alternate
Port 2525 is widely used as an alternative SMTP (Simple Mail Transfer Protocol) port for email message submission, particularly as a workaround when ISP restrictions or firewall policies block the default SMTP port 25. While unofficial, it has become popular among email service providers for facilitating reliable outbound email delivery..
SMTP Alternative Port: Port 2525 is an unofficial yet highly popular alternative to the traditional SMTP port 25. It supports reliable message relay and submission using standard SMTP commands, often leveraged to ensure email delivery when port 25 is blocked or filtered by ISPs or network security devices.
Functionality: The port can handle message submission from client mail agents (MUAs) to mail server systems (MTAs or MSAs). It supports standard SMTP extensions including TLS for encryption (if configured), authentication (e.g., LOGIN, PLAIN, or CRAM-MD5), and queue management.
Compatibility: Many email service providers explicitly support port 2525 interchangeably with ports 25, 465, or 587. It is not officially designated by IANA, but its use helps alleviate issues arising from anti-spam measures that limit port 25 traffic. Configuration requires proper server support on this port for message acceptance.