iOS IMAP Connection Issues Resolved

In the last few days, I’ve spent hours and hours configuring accounts on my private iPhone 6 running iOS 11 in order to attempt to nail down where its connection issues originate.

I’m happy to be able to tell you I seem to have nailed it down, and there’s a quick fix for it, that we can apply on the server-side.

The TL;DR is RFC 5819, aka. LIST-STATUS, does not function in a Cyrus IMAP discrete Murder environment.

The immediate workaround is therefore to suppress the capability, as I have just done, for which Apple must have enhanced the IMAP client stack in iOS 11 (compared to iOS 10), so that large folder listings need to be iterated over less.

The underlying cause is the nature of information that a Cyrus IMAP frontend holds about individual mailboxes — it’s basically which exist, who’s got access, and where they live. It doesn’t hold status information about each mailbox, so it would need to connect to backends to retrieve the information — it doesn’t.