I currently administer a corporate network. We have a single email server on our corporate network. We receive emails through our ISP. They come through to our exchange 2013 on the inbound connector. Emails going out are set to our ISP through smtp2x.isp.com. My current MX records show the following:
corporate.com. 86400 IN MX 5 mail.corporate.
corporate.com. 86400 IN MX 10 vmx1.isp.com.
I am able to send emails to all domains but about 2 weeks ago I started receiving the same error message for emails sent to 3 particular domains:
The following message to <firstname.lastname@example.org> was undeliverable.
The reason for the problem:
5.1.0 - Unknown address error 553-'SPF (Sender Policy Framework) domain authentication\nfail. Refer to the Troubleshooting page at\nhttp://www.symanteccloud.com/troubleshooting
for more\ninformation. (#5.7.1)'
I suspect that it could relate to my SPF records in my zone file but am not receiving any assistance from my ISP who hosts my zone file. I am trying to implement SPF to address this issue.
Any assistance would be greatly appreciated.