Block spam from subdomains

Created: 2015-10-13 — modified: 2016-12-11 — tags: e-mail

If you have a domain and don't want to be blocked for sending spam.

If you're a proud owner of your own domain (say, example.com), and have an email address with it, then you probably know what are SPF-records and how to use them to prevent other people getting unwanted messages with your address in the "From" field.

But one day you may learn (usually by getting a "bounce" email) that spammers can send emails from subdomains of your main domain (say, bill@office.example.com).

That's not nice, because: a) other people are getting spam, and b) your domain gets visible by anti-spam filters.

To somehow prevent or limit this, you can simply add this wildcard SPF record to your DNS system:

* IN TXT "v=spf1 -all"

It will tell all email servers that respect SPF that they should reject all mail coming from all subdomains of your domain.

Source: http://www.openspf.org/FAQ/The_demon_question