imapc fetch optimization

Hi,

imapc does a lot of UID FETCH $UID (BODY.PEEK[]), which is nice, because it works even with the dumbest IMAP server, altough it really kills performance, especially on high latency lines.

I wonder: if IMAP servers can effectively handle boundless fetches (like a list with all wanted UIDs, or simply 1:* if all are needed), do you see this as a good addition to develop?

This could be a new imapc_features setting afterall...

Thanks,