Which is not a standard communication port for SMTP traffic?

Which is not a standard communication port for SMTP traffic?

• 465
• 110
• 587
• 25 

EXPLANATION

Communication between mail servers generally uses the standard TCP port 25 designated for SMTP

Mail clients however generally don't use this, instead using specific "submission" ports.
Mail services generally accept email submission from clients on one of:

• 587
• 465

SOURCE

https://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol