UID was introduced in IMAPv4 in RFC 1730 in 1994, and it's not optional for IMAPv4 or IMAPv4.1
I last wrote IMAP server-side software in 2000. Even then, I was not aware of any IMAP servers that didn't support UID. It was essential, as most clients expected it to be there.
There might still have been some at that point, but I'd be shocked if anyone is still running any IMAP2 or IMAP3 servers.
I last wrote IMAP server-side software in 2000. Even then, I was not aware of any IMAP servers that didn't support UID. It was essential, as most clients expected it to be there.
There might still have been some at that point, but I'd be shocked if anyone is still running any IMAP2 or IMAP3 servers.