IMAP - difference between msgno and uid?

Question

What is the difference between msgno and uid? It looks like they always are the same even if msgs are deleted!?

Answer 1

As it says on http://www.php.net/manual/en/function.imap-uid.php:

This function returns the UID for the given message sequence number. An UID is a unique identifier that will not change over time while a message sequence number may change whenever the content of the mailbox changes.