- issues where folders (e.g. deleted, sent) get duplicated
This is only likely where the IMAP clients has not been configured properly ... or one uses a poor IMAP client such as Win10 Mail which insists on its own naming convention for folder names (certainly the sent items folder). If all IMAP clients use the IMAP server folders, there ought to be no duplication.
Using client side rules only needs to be configured on one always on client ... and the operational issues you mention, ought not to be prolific ... and if they were to occur not long lasting ... would a short delay in moving a mail be that detrimental? I have one email client which does some of my filing for me me ... if it get delayed by an hour or two, the wheels do not fall off!
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