Problem to receive some emails from a particular domain

Products

• Email Security.cloud

Issue/Introduction

You are facing an intermittent issue with receiving emails from a particular domain. Some emails are quarantined by Anti-Spam Service - filtered by DMARC. Sender policy of domain.com (p=quarantine adkim=r aspf=r).

Environment

Email Security.cloud

Resolution

Start analysis with the following article: Emails from particular domain are blocked and check the SPF and DMARC records for the sender. If in the SMTP log you notice the error below, check the nameservers for sender's domain:

! An error has occurred during SPF processing (SPF_errcode: 26): DNS lookup failure

If the authoritative name servers (NS) are not set up correctly for DNSSEC, we may have intermittent lookup failure and this cause our resolver not trusting the results returned from sender's name servers and give us SERVFAIL error.
The issue needs to be resolved on the sender's side.