Adding TLS to SMTP, POP3, and IMAP is no different than adding TLS to HTTP. Similar to how HTTP gets an appended S for Secure and becomes HTTPS, SMTP, POP3, and IMAP become SMTPS, POP3S, and IMAPS, respectively. Using these protocols over TLS is no different than using HTTP over TLS; therefore, almost all the points from the HTTPS discussion apply to these protocols.
The insecure versions use the default TCP port numbers shown in the table below:
| Protocol | Default Port Number |
|---|---|
| HTTP | 80 |
| SMTP | 25 |
| POP3 | 110 |
| IMAP | 143 |
The secure versions, i.e., over TLS, use the following TCP port numbers by default:
| Protocol | Default Port Number |
|---|---|
| HTTPS | 443 |
| SMTPS | 465 and 587 |
| POP3S | 995 |
| IMAPS | 993 |
TLS can be added to many other protocols; the reasoning and advantages would be similar.