I do not have a crystal ball to see why the website has been blocked by avast. Only an Avast Team Member can tell us and also whether it will be unblocked by him, as we cannot as we are just volunteers with relevant knowledge.
The blacklisting seems unlikely as it is an old McAfee blacklisting, that not even Google Safebrowsing has now.
More likely there is a block because of mail servers that have inconsistent reverse DNS entries (the word of the game SPAM block).
Connect to Mail Servers
FAIL: Connection to all mail servers failed.
-dc-5dc711c9.cuaca.co.id.: dial tcp -45.63.93.149:25: getsockopt: connection refused
To receive emails, mail servers should allow TCP connections on port 25.
and
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
dc-5dc711c9.cuaca.co.id. 45.63.93.149 45.63.93.149.vultr.com. ?
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.
All IP’s reverse DNS entries should resolve back to IP address (IP → PTR → IP). Many mail servers are configured to reject e-mails from IPs with inconsistent reverse DNS configuration.