The UIDL extension adds a "UID" but it's just an MD5 hash of the contents -- meaning that multiple copies of a message appear to be the same message.
That sounds like a server problem; to quote the RFC,
The server should never reuse an unique-id in a given maildrop, for as long as the entity using the unique-id exists.
Why would you hash the contents? The arrival time should be unique, assuming no two messages could arrive at exactly the same time. That doesn't require any hashing.
I think POP could've been far better designed, without growing into the complexity of IMAP, with just a few little changes like this.
That sounds like a server problem; to quote the RFC,
The server should never reuse an unique-id in a given maildrop, for as long as the entity using the unique-id exists.
Why would you hash the contents? The arrival time should be unique, assuming no two messages could arrive at exactly the same time. That doesn't require any hashing.
I think POP could've been far better designed, without growing into the complexity of IMAP, with just a few little changes like this.