I think you meant "NOTIFY without an IDLE fallback".
The problem with IDLE is that you need a separate connection for each mailbox. So if you want all email in sync, you need N connections for N mailboxes. Plus separate connections to do the actual syncing, because IDLE takes makes a connection unusable for anything else. Or need to compromise in that some (most) mailboxes will be "polled" ever M minutes.
Fortunately, all of the email providers to which I have access support the required capabilities. Consider asking your service provider to upgrade; the newest standard required by ImapGoose was standardised in 2009.
The problem with IDLE is that you need a separate connection for each mailbox. So if you want all email in sync, you need N connections for N mailboxes. Plus separate connections to do the actual syncing, because IDLE takes makes a connection unusable for anything else. Or need to compromise in that some (most) mailboxes will be "polled" ever M minutes.
Fortunately, all of the email providers to which I have access support the required capabilities. Consider asking your service provider to upgrade; the newest standard required by ImapGoose was standardised in 2009.