How to test mail server dkim, spf, tls, ssl after setup

I'd share a bunch of tools i use for test mail server setup.

SSL Certificate and TLS

First of all test if server establish ssl connections.

openssl s_client -connect -starttls smtp  

Next step is test TLS and check does certificate is valid with very handy tool:

DKIM, SPF checks

There is service to check mail authorization, simple send email to it:

echo "hi" | mail -s "testme"  

it should send results back to you then.

As well, there is more options such as extracting gmail headers information and so on, listed methods above is enough in my case.