Two Sections

Section A

POP3 allows users to fetch and download e-mails from a remote mailbox. Does this mean that the internal format of the mailboxes has to be standardized so any POP3 program on the client side can read the mailbox on any mail server?

Section B

1. DNS uses UDP instead of TCP. If a DNS packet is lost, there is no automatic recovery. Does this cause a problem, and if so, how is it solved?

2. Suppose that someone sets up a vacation reply and sends a message before logging out. Unfortunately, the recipient has also set up a vacation reply message. What will happen in this case? Will the canned replies keep on going back and forth until someone returns?

3. When web pages are sent out, they are prefixed with MIME headers. why?

4. Does VoIP have same the problems with the firewall that streaming audio has?