When troubleshooting email delivery, it is essential to know what the SPF (Sender Policy Framework) and the DMARC (Domain-based Message Authentication, Reporting & Conformance) records are for the domain. 

You can lookup records from the Command Line:

Dig and NSLookup are two common command line tools to lookup DNS records.

To lookup DMARC:

dig txt _dmarc.[EXAMPLE.COM]

or 

nslookup -type=txt   _dmarc.[EXAMPLE.COM}

To Lookup SPF records:

nslookup  -type=txt [EXAMPLE.COM]

or

dig txt [EXAMPLE.COM]

You can also use the MXtoolbox website to lookup and test email delivery: https://mxtoolbox.com/SuperTool.aspx