Looked into your DNS and found: Reverse Entries for MX records
WARNING: Found mail servers with inconsistent reverse DNS entries. You should fix them if you are using those servers to send email.
Server IP PTR (Reverse) IPs
mail.eu.pn. 185.176.40.125 ? ?
All mail servers should have a reverse DNS (PTR) entry for each IP address (RFC 1912). Missing reverse DNS entries will make many mail servers to reject your e-mails or mark them as SPAM.
Maybe that was the reason to block it?
Wait for an Avast Team Member to give a verdict here, as we are just volunteers and they do the unblocking.