Port 587: Submission
Port 587 is the standard mail submission port for clients sending outgoing mail. It upgrades to TLS with STARTTLS and requires authentication, which is why providers prefer it over port 25.
TCPEmail EncryptedIANA assigned
| Port number | 587 |
|---|---|
| Service | SMTP mail submission (STARTTLS) |
| Protocol | TCP |
| Category | |
| Default encryption | Yes (TLS/SSH) |
Frequently asked questions
What is port 587 used for?
Port 587 is the standard mail submission port for clients sending outgoing mail. It upgrades to TLS with STARTTLS and requires authentication, which is why providers prefer it over port 25.
Is port 587 TCP or UDP?
Port 587 (Submission) uses TCP.
Is port 587 secure?
Yes. Port 587 carries encrypted traffic by default, so data in transit is protected.
Should I open port 587 on my firewall?
Only if you specifically need Submission. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.