kFetchHeader
IMAP::kFetchHeader | IMAP::kFetchFlags);
if ((fetchFlags & (IMAP::kFetchHeader | IMAP::kFetchBody))
== (IMAP::kFetchHeader | IMAP::kFetchBody)) {
} else if ((fetchFlags & IMAP::kFetchHeader) != 0) {
case kFetchHeader:
kFetchAll = kFetchHeader | kFetchBody,
flags = IMAP::kFetchHeader;