What is the difference between port 465 and port 587?

Port 465 establishes TLS encryption immediately before sending SMTP commands (Implicit TLS). Port 587 starts in cleartext and upgrades to TLS via STARTTLS (Explicit TLS).

Which port is recommended for sending email: 465 or 587?

RFC 8314 recommends Port 465 with implicit TLS as the modern best practice, although Port 587 remains universally supported across all email providers.

How do I test if my mail server port 465 is reachable?

Run an open port check with our tool or execute 'openssl s_client -connect mail.example.com:465' to verify SSL negotiation.

Home/Open Port Checker/Port 465

Port 443 Port 587

Well-Known Port Reference

Port 465: SMTPS (SMTP over SSL) (TCP)

Implicit TLS-encrypted Simple Mail Transfer Protocol submission channel for email clients.

Port Number

465

Transport

TCP

Security Risk

Low

Standard / RFC

RFC 8314

Test Port 465 Reachability Live

Verify whether Port 465 is open, closed, or filtered on your server or public IP address.

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Service Architecture & Function

Port 465 was originally allocated for SMTPS (implicit TLS email submission). While briefly deprecated in favor of STARTTLS on port 587, RFC 8314 officially reaffirmed port 465 as the recommended standard for client-to-server email submission wrapped in implicit TLS from the first packet.

Security Profile & Hardening

Because TLS negotiation begins immediately upon connection establishment, port 465 prevents plaintext downgrade attacks that can theoretically affect STARTTLS sessions.

Example Firewall Commands:

# UFW (Ubuntu/Debian)

sudo ufw allow 465/tcp

# iptables (Direct Kernel)

iptables -A INPUT -p tcp --dport 465 -j ACCEPT