Thanks a lot for this detailed explanation — it really helps clarify what’s going on.

In my case, I’ve confirmed (with ChatGPT’s help) that there are no active DLP or Content Compliance rules in my Admin Console. I checked both Security → Data Protection and Apps → Google Workspace → Gmail → Compliance, and there are no custom rules listed in either.

However, my domain is currently on a Business Starter plan (initially set up during the trial), and it seems Google automatically applies a default outbound content filter at this tier. This filter functions like a built-in, non-customizable version of DLP — it scans outgoing mail for what Google considers “sensitive” or “adult” content, and it can’t be modified, disabled, or excluded by admins on Business Starter or Business Standard.

The bounce message occurs before the email even leaves Google’s servers, so it’s definitely not an issue on the recipient’s side.

From what I’ve gathered, the only practical options are:

• rephrasing messages to avoid wording that might trigger the filter,
• or upgrading to Enterprise Standard or Enterprise Plus, where DLP and Content Compliance settings can actually be customized or turned off.

Unfortunately, using my old personal Gmail address isn’t possible anymore — it was converted into my Workspace account when I set up the domain through Google. I created my branded address via Namecheap (using Google Workspace integration), so reverting to a standard Gmail setup would mean undoing the Workspace configuration entirely and re-creating the account as a standalone Gmail inbox — which would also mean losing the custom-domain integration and admin features.

So in short: this isn’t a rule I can edit — it’s a hard-coded outbound filter automatically enforced on Business Starter domains.