All of these are general ports used for email except which one?

All of these are general ports used for email except which one?

• 25
• 22
• 587
• 110           

EXPLANATION

Common port numbers

Main article: List of TCP and UDP port numbers

The Internet Assigned Numbers Authority (IANA) is responsible for the global coordination of the DNS Root, IP addressing, and other Internet protocol resources. This includes the registration of commonly used port numbers for well-known Internet services.

The port numbers are divided into three ranges: the well-known ports, the registered ports, and the dynamic or private ports.

The well-known ports (also known as system ports) are those from 0 through 1023. The requirements for new assignments in this range are stricter than for other registrations, examples include:

• 20: File Transfer Protocol (FTP) Data Transfer
• 21: File Transfer Protocol (FTP) Command Control
• 22: Secure Shell (SSH) Secure Login
• 23: Telnet remote login service, unencrypted text messages
• 25: Simple Mail Transfer Protocol (SMTP) E-mail routing
• 53: Domain Name System (DNS) service
• 80: Hypertext Transfer Protocol (HTTP) used in the World Wide Web
• 110: Post Office Protocol (POP3)
• 119: Network News Transfer Protocol (NNTP)
• 123: Network Time Protocol (NTP)
• 143: Internet Message Access Protocol (IMAP) Management of digital mail
• 161: Simple Network Management Protocol (SNMP)
• 194: Internet Relay Chat (IRC)
• 443: HTTP Secure (HTTPS) HTTP over TLS/SSL

The registered ports are those from 1024 through 49151. IANA maintains the official list of well-known and registered ranges. The dynamic or private ports are those from 49152 through 65535. One common use for this range is for ephemeral ports. 

SOURCE

https://en.wikipedia.org/wiki/Port_(computer_networking)