In addition to Kyle suggestion of using mxtoolbox, to check if your dkim/spf/dmarc settings are working correctly, you can send a mail to check-auth@verifier.port25.com, from an account on the domain you want to verify.
It will reply back with diagnostics results.
IMHO this method is better as it also checks, for DKIM, if the server uses the right key to sign the mail.
Mxtoolbox only check if the DNS entry is valid but not if the server actually signs the mail correctly with the corresponding key.
It was very useful to me to find out for some customers that their DNS dkim declaration didn't match the key generated by the server.
Sébastien Riccio
System & Network Admin
https://swisscenter.com