This is a very handy tool for email servers with multiple queries to diagnose if your email server works properly:

If you want to run a sane email server, this is your go tool.

hyperlinks

This is a very handy tool for email servers with multiple queries to diagnose if your email server works properly:
- MX records
- DMARC, PTR, SPF (I saw many email servers with improper sets for these 3 and that end up in spam lists)
- Blacklists

and many more.
If you want to run a sane email server, this is your go tool.