I just finish configuring my own mail server using this guide: LinuxBabe Guide
At the start all was working but now I can not receive mail from external. Here is my configuration file: https://hatebin.com/npslpqyqpr
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Your name appears to have a dozen or more IPv6 addresses set in the DNS, but as far as I can tell none of them actually respond on any port. Mail providers which also use IPv6 (such as Google or Microsoft and many others) will try those addresses and get a timeout, then queue the mail to try again later.
Your server does answer SMTP on IPv4, but it can take hours or even days before the mail sender gets around to trying the IPv4 address.
You should either fix your IPv6 connectivity or remove the AAAA records from your DNS.