Question about POP3 protocol
 

I'm developing email client and here's my problem...When i connect to the mail account and download all headers and then close the application obviously i want next time when i start the application to populate already downloaded headers and download only these headers which are not downloaded before.I can do that but the problem is i don't know how to associate number to every of the downloaded headers,i mean the number needed for downloading the corresponding letter with the RETR command.I mean when i connect to the account,if i delete few letters then the numbers of all letters in that account are changed.Right?Sorry if i'm wrong but i think that's how the pop3 protocol works.Actually i'm not sure whether this is problem of the pop3 protocol or is problem of the mail account(s).Sorry for my bad english too.Can someone help me with that?

Welcome the the EMD forums, cygnusX88!

I'm just taking a guess here - but I would expect that messages are identified by a message-ID that doesn't change, not serial numbers that would change after every deletion. (POP3 has been used successfully for too long a long time for the protocol to be a problem :) ) Can you find a message-ID associated with each of the headers you downloaded?

Thanks,but after some research i found that this "message-id" can't help me in that situation.I found also that i can use the UIDL command to give the proper number to every letter in the mailbox.

"...Most POP3 commands identify specific messages by their ordinal number on the mail server. This creates a problem for a client intending to leave messages on the server, since these message numbers may change from one connection to the server to another. For example if a mailbox contains five messages at last connect, and a different client then deletes message #3, the next connecting user will find the last two messages' numbers decremented by one. UIDL provides a mechanism to avoid these numbering issues. The server assigns a string of characters as a permanent and unique ID for the message. When a POP3-compatible e-mail client connects to the server, it can use the UIDL command to get the current mapping from these message IDs to the ordinal message numbers..."

Good digging! Thanks for the feedback and sorry for the dead-end lead.