is there restriction for opening imap connection from same ip address?

Question

Hi I am implementing Email Client Application. My requirement is i need to monitor all the mailboxes available in specified IMAP server. I am created separate TCP Connection for each mailboxes. But i am getting disconnected from IMAP Server. I am trying Gmail/yahoo for my testing purpose. Is there any restriction to open multiple connection from same ip to particular IMAP Server? Particularly in Gmail and Yahoo.

or is there anyway to Monitor all the mailboxes in Single Connection without using IMAP-NOTIFY seems it does not supported in both Gmail/Yahoo...

Please Help me out...

Answer 1

This is something which I have answered on stackoverflow before, but which is now only available via the wayback machine. The question was about how to "kill too many parallel IMAP connections". Reprinted below; the core takeaway message is that for some reason, most server administrators prefer to have smaller number of short-lived connections instead of more connections which are active over longer period of time, yet they spend most of their time silently idling in the background. What they do not get is that the IMAP protocol is designed with long-lived connections in mind, and trying to prevent that will lead to wasting resources because the clients will constantly resync mailboxes as they are hopping among them.

The original answer follows:

Nope, it's a very wrong idea. IMAP is designed so that monitoring a single mailbox takes one connection; in most IMAP server implementations, this means a single process. However, unless the client the user is using is terribly broken, all these connections enter the IDLE mode. In IDLE, the clients are passively notified about any updates to the mailbox state. If you disable these connections, the clients would have to activelly poll for changes in many mailboxes. Now decide for yourself -- what is worse, having ten processes sitting idle, or one process doing heavy polling every two minutes? Which of these solutions would consume more energy, CPU time and IO operations? That's for the number of parallel connections.

The second question was about the long-lived connections. Again, this is a critical aspect of IMAP -- each connection carries a lot of associated state information which is rather expensive to obtain. Unless your server implements certain extensions and your clients use them (ESEARCH, CONDSTORE, QRESYNC are the crucial bits), opening a mailbox can require O(n) operations. I don't know how many messages your users have, but do you really want to transfer e.g. message flags for 250k messages when you decided to kill a connection because it has been active for "too long"?

Finally, any reasonable IMAP server vendor offers a way to configure a per-user session limit on the number of concurrent processes. Using that is much better than maintaining a script for ad-hoc killing of "unused" connections.

If you would like to learn more about the synchronization process, my thesis about using IMAP on clients with flaky network and limited resources describes what the clients have to do in order to show an updated view of mailboxes to their users.