Help with Mail: Postfix + SpamAssassin + TLS

I'm at my wits end here. I have a small server running VirtualMin with a dozen or so hosts. Email is working and not on fire, but not configured great.
I've setup Let's Encrypt certs, and they are working generally. I'm Looking to hire help for:

1. SSL/TLS working for SMTP
2. SMTP sending working consistently (iPad, iPhone act wierd)
3. Spamassassin & ClamAV working (they are setup in Virtualmin, but don't appear to be doing much).

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Thanks! 'Brian