sender rejected, envelope sender domain could not be resolved

[Michael Bale]

Out of nowhere, we started to receive this error for lots of incoming mail.  We are using DNS Verification (now off) w/ root DNS servers.  I am using Virtual IronPort devices.

What would cause this to start happening out of nowhere?

[Ken Stieers]

Feels like a DNS resolution issue. First thing I would do is get off the root DNS servers.
Try one of the other public ones instead.

There is a list here: https://www.lifewire.com/free-and-public-dns-servers-2626062

[Michael Bale]

I've been using root servers for like 14 years, never had a glitch, and we had a big glitch today where it was throwing DNS verification errors constantly for multiple domains.

[Ken Stieers]

<shrug> I don't know.. all I'm going on is that you stared that your sender verification stuff started failing lots of mail... all of the sender verification stuff (spf/dkim/dmarc/reverse lookup) is DNS based...

Is outgoing mail going? (Monitoring/Delivery Status)