Many ports are reserved for common functions (22 and 53 are always ssh and dns), but many are used for different things altogether (8080 for instance can be used for many different services across many different vendors/developers).

IANA maintains the list of reserved ports when dealing with internet, and can be found at their website (along with other lists such as top level domains, IP address allocation, etc.) https://iana.org/

Fun fact for anyone who gives a shit:

For standard mail access and transmission, ports 25 (SMTP, sending) and 143 (IMAP, receiving) have been largely replaced by 587/465 and 993 respectively to facilitate SSL/TLS encryption. In some cases IMAP is absent from primary use and may be disabled by default (Microsoft, where Exchange services are primary, and Google, where MAPI is heavily utilized), but are still available for compatibility purposes.

Some legacy services still utilize 25 for sending alerts, but most everything recent allows for SMTPS for mail-enabled services.

The more you know (cue the rainbow ->🌈)

“Thunderstruck is not an AC/DC song. Back in Black is an AC/DC song, but Thunderstruck doesn’t sound like it, therefore it isn’t by them.”

—Stockag, probably

That’s a really long name for a Gorillaz song.