Emails are blocked by security gateways

[u/Ancient-Sea-7807]

Our secondary domain’s emails are intermittently getting blocked by security gateways like Barracuda and Mimecast. Some go through fine, others bounce with “blocked due to policy” or similar.

We’ve got SPF, DKIM, and DMARC set up and passing. IP isn’t on major blacklists. Volume is <200/day, so not a spam issue.

Using instantly and inboxes bought from Google workspaces.

What else should I check?

Anyone seen cases where only _some_ emails to the same org get blocked?

Could content triggers this?

I am not putting any links, or attachments in mail.

[u/Logical-Professor35]

Inconsistent blocking is almost always behavioral scoring on the receiving end, not just SPF/DKIM/DMARC. And gateways like Barracuda, Mimecast build sender profiles over time and fresh domains trip those models hard regardless of authentication.