My mail server is set up so that every email to the domain comes to me. One can email whatever_they_want@mydomain.com, and it will forward to me.

I often get spam to strange address. Let's say, Bob_White@mydomain.com - just random names. I get a lot of these, always to different names. On any other mail server, the invalid address would just bounce back to the spammer. So why am I getting spam to these addresses?

  • 2
    Note that generally an invalid address should not send a bounce to the spammer, but fail in the same connection, since otherwise it will be sending the bounces to innocent parties whose email was spoofed! – Ángel Sep 3 '17 at 21:57

I can see at least two reasons.

The first is that spammers know that a number a people like you turn on catchall E-mail. So they are trying their luck.

Second, in addition to using know E-mail addresses, spammers will also fetch lists of domain names and try more or less random combinations. They will of course try info@domain.tld, sales@domain.tld, webmaster@domain.tld, etc but may also use common name/surname combinations. It's some sort of brute-force spamming.

The aim is to reach a maximum number of recipients.


Few Best Practices to configure on your Email security gateway ti avoid your situation:

1 - Drop the mails with the unknown user (email) - you may sync the Email Security Gateway with the Directory Service or your mail server.

2 - Do not send bounce messages - this would allow spammers to validate the legitimate yours on your mail server. And If spammers sending spoofed email addresses the real users will receive unwanted return messages

3 - Configure your Email Security gateway for threat intelligence feeds where the blacklisted IPs/Domains could be blocked without spamming you.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.