Port 587: SMTP submission (listed as SMTPS on Network+)

What is port 587 used for?

Port 587 is the mail submission port: the one an email program, a phone or a device such as a scanner uses to hand outgoing mail to its provider's server, after signing in.

Submission was separated from port 25 so that providers could apply different rules: on 587 the sender must authenticate, and the connection is upgraded to TLS with STARTTLS before the password is sent. CompTIA's Network+ objectives label 587 as SMTPS. Outside the exam, 587 is known as submission with STARTTLS, and the port where TLS starts immediately, with no upgrade step, is 465. For the exam, learn 587 as the secure SMTP port.

Is port 587 TCP or UDP?

TCP. Message submission is SMTP with sign-in, and like all SMTP it runs over TCP, here on port 587.

Is port 587 encrypted?

It starts in clear text and the client upgrades it with STARTTLS before signing in; a correctly configured client refuses to continue if the upgrade fails. Port 465 is the alternative where TLS is in place from the first byte.

Port 587 vs port 465: what is the difference?

Both are for submitting outgoing mail with sign-in. On 587 the session is upgraded to TLS with STARTTLS. On 465 TLS is implicit, from the first byte. RFC 8314 registers 465 for this and recommends implicit TLS, while 587 remains widely used.

Which CompTIA exams list port 587?

CompTIA lists port 587 by number in the Network+ objectives; the A+ Core 1 port list does not include it.

• Network+ N10-009: objective 1.4 (Networking Concepts), listed as “Simple Mail Transfer Protocol Secure (SMTPS), 587”.

The quoted text is how the objectives document lists the port. The exam puts the port in a scenario, such as a firewall rule or a failed connection; it does not only ask for the number.

Check yourself: a practice question

Written by CertSprint for this page. It is not taken from any exam.