Comment 50 for bug 119899

There were other reasons to switch it - e.g., filters that check if a sender is in an address book only work locally, not on the imap server. Filters run locally tend to be a lot faster, though that's less important than correctness, obviously. Either way, some filters aren't going to work after the fact without some non-trivial re-working of the search backend. Either we could store the custom headers in the .msf files as msg hdr properties and allow local search to work with those properties, or we could figure out how to do hybrid searches, partly locally, partly on the server. I've been leaning to the former, so that things like views on custom headers can work with imap as well.