Like Going to the Post Office

For a long time it's been true that the average personal computer is not well-suited to running highly available public facing services. In the original model for network mail delivery though, everyone that wanted to receive mail needed a local mail transfer service. The increasing use of individual workstations rather than shared servers made this problem particularly acute. Two protocol families emerged to deal with the problem and allow access to a remote mail store: the Post Office Protocol and the Interactive Mail Access Protocol.

The dominant mail protocol for quite a while ended up being the third version of the Post Office Protocol, also called POP3. Twenty years ago was the first release of the POP3 protocol, based on the earlier POP and POP2 protocols. POP3 interacts with a mail user agent running on a standalone workstation to manage mail stored by a mail server. You can read more about the details of the POP3 protocol in RFC 1081.

To give a comparison with mail systems at the time, the IMAP specification published a few months earlier described an implementation with limits of 6.75 MB for a mailbox and 18,432 total messages. Since these limits were much larger than the capabilities of existing mail programs, it was expected that no one had yet to encounter them.