Q2150040: I have 10 messages in my POP3 mailbox, with Message IDs [1..10]. When I delete message , do the Message ID's of message [6..10] change?
No, the Message ID's do not change. This is because the message is actually not deleted, but marked as deleted. It will be deleted as soon as the connection is broken. So, in your situation after deletion, you will have the following valid Message ID's: [1..4] and [6..10].