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SMTP over SSL
Port 465 is commonly used for secure SMTP communication, encapsulating email transmission within SSL encryption. This port facilitates encrypted email delivery between clients and mail servers, enhancing privacy compared to traditional plain-text SMTP connections. Although it was initially designated as a secure SMTP port, its status has shifted over time, but it remains widely supported for legacy encrypted email connections..
SMTP over SSL, associated with port 465, was originally registered for secure SMTP submissions where SSL/TLS encryption is used to protect email exchanges. Unlike opportunistic STARTTLS, which upgrades an insecure connection, SMTP over SSL initiates a secure, encrypted connection from the outset known as implicit TLS. This design ensures all communication on the connection remains confidential and resistant to passive eavesdropping.
Historically, port 465 was briefly assigned as the standard for SMTPS. However, this designation was revoked in favor of submission via port 587 using STARTTLS. Despite its deprecated official status, many email service providers continue supporting port 465 as a default for implicit SSL/TLS due to widespread client compatibility and legacy support.
Modern email infrastructure typically favors port 587 or 25 with STARTTLS for MTA-to-MTA and client-to-server interactions. Yet, port 465 persists as a method of securely conveying credentials and message data during submission, especially in older or consumer-grade email clients. Administrators should be aware of its deprecated status but also recognize its ongoing practical usage.