How to Block Mail to a Google Workspace Catch-all Address

Catch-Alls are Cool

Are you using Google Workspace (formerly Gsuite) for email service? If you do, you might want to configure the domain as a “catch-all.” Meaning mail to any address is accepted and delivered to the main mailbox (or whatever address you specify). I find this very handy. It lets you create unique addresses on the fly (with no prep -- just submit a new address to a form and you know it'll be deliverable), and track where your email address ends up. But what happens when an address you’ve used ends up in the wrong hands? Here’s where a quick change to Gmail’s Default Routing configuration can come to the rescue.

This handy trick lets you reject mail to a specific address with a 5xx "no spam" response instead of just filtering it out of view. Why is this better? Because filtering just hides the problem from view, while rejecting lets bad senders know they’re blocked. Maybe, just maybe, they’ll suppress your address from future sends (or at least stop trying to get through).

How to Set It Up

Blocking mail to a specific address is easy. Just follow these steps:

1. Go to Gmail’s Default Routing configuration page.
2. Add a new rule.
3. Specify the (destination) email address that you want to block.
4. Change the action to "Reject" and add an error message (something like "No spam allowed!")
5. Choose to match both known and unknown senders.
6. Save the rule.

And just like that, unwanted email to that address will bounce with a 5xx SMTP response, including whatever customized text you specify.

Why This Is Useful

If a particular address gets flooded with unwanted mail, you don’t have to disable your whole catch-all setup. Just shut off mail to that one address. No more junk slipping through, no extra filtering rules needed.

Want to see this in action? Go ahead and send an email to plotz@spamresource.com and you can see this very process first hand. Your message will get bounced back, based on a routing rule I've created.

I have somewhere around 45 of these configured for my own email domains. It’s so handy, allowing me to continue to run a catch-all configuration while being able to blocking spammers when addresses leak.

And while I do also block senders, not just specific recipient addresses, this method has the added perk of not mattering who the sender is. Often, a particular unique address will start getting spam from multiple addresses, either multiple spammers, or one spammer changing up their address repeatedly. Either way, I’m good. That particular door is closed.