Pop3.DeleteMessageByUID(uid) does not work

Question

On some servers, the method Pop3.DeleteMessageByUID(uid); does not work.

There are no error messages, but nothing happens, the mail is still there.

What can be causing this problem?

Answer 1

1. Remember to use Close method, as DeleteMessageByUID only marks
   message for deletion. Message is actually deleted after successful
   QUIT command is received by the server. Close sends QUIT.

2. Some servers behave differently than the standard describes.
   For example Gmail:
   https://www.limilabs.com/blog/gmail-pop3-behavior