Application Development Software

I am planning to migrate the JES 2004Q2 to JES5. I am worried about whether user would lose messages after migration, if they select "leave a copy of messages on server" using POP3.

source from wikipedia [ [http://en.wikipedia.org/wiki/Post_Office_Protocol|http://en.wikipedia.org/wiki/Post_Office_Protocol ]

Clients with a leave mail on server option generally use the POP3 UIDL (Unique IDentification Listing) command. 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. The client can then use this mapping to determine which messages it has yet to download, which saves time when downloading. IMAP has a similar mechanism, a 32-bit unique identifier (UID) that must be assigned to messages in ascending (although not necessarily consecutive) order as they are received. Because IMAP UIDs are assigned in this manner, to retrieve new messages an IMAP client need only request the UIDs greater than the highest UID among all previously-retrieved messages, whereas a POP client must fetch the entire UIDL map. For large mailboxes, this difference can be significant.