Port 587 · SMTP Submission

Port 587 is SMTP Submission, TCP.

Mail submission with STARTTLS — preferred port for email clients submitting to their outbound mail server.

Palo Alto

Create the service object for this port, then allow the App-ID on it. Restricting the rule to the port's service object keeps the rule working on a non-default port and stops the App-ID matching on other ports. Replace the placeholders with your own rule name and zones.

set service tcp-587 protocol tcp port 587

set rulebase security rules <rule-name> from <from-zone> to <to-zone> source any destination any application smtp service tcp-587 action allow

Risk and exposure

Rated low risk. Even so, only expose this port to the networks and hosts that need it, and keep it patched.

Check it

• Linux ss -tlnp | grep :587
• PowerShell Test-NetConnection <host> -Port 587
• nmap nmap -p 587 <host>

Related ports

• 465 SMTPS
• 25 SMTP
• 110 POP3
• 143 IMAP
• 993 IMAPS
• 995 POP3S

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