[Imap-protocol] Unsolicited server responses

Arnt Gulbrandsen arnt at gulbrandsen.priv.no
Fri Nov 30 03:56:24 PST 2018

>> Given that the server can unilaterally send updates to the

>> client, why was the IDLE extension useful/necessary?


> I'm no expert but I don't think I have seen an IMAP server that

> sends unsolicited EXISTS or EXPUNGE responses when not in IDLE

> mode.

I've co-written one that sends a sends a very small number of responses and
then stops, which hasn't caused problems. I've heard that another server
sent an unlimited number of responses using blocking i/o, and that would
cause problems if the client wasn't listening.

IIRC more servers send unsolicited responses occasionally, to keep NAT
middleboxes from discarding the connection.

> "While the spec [RFC3501 I assume] actually does allow a server

> to push EXISTS responses asynchronously, a client can't expect

> this behavior and must poll."

That's the key.


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