How do I accept e-mail that’s being rejected with a “Domain not found” error?

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If someone sends you mail from an address like “address@x.y.z.example.net”, and “x.y.z.example.net” is not an actual “hostname” in the Internet’s DNS system, our spam filters will usually reject that mail.

The fact that it’s not a real hostname means the message violates Internet mail standards and appears to be forged. This is something that only spammers usually do, so our servers (like most other mail servers) will reject it.

The proper solution in such a case is for the sender to either add “x.y.z.example.net” to the DNS system, or to change the mail sending address to match a hostname that already exists. If that can’t be fixed, though, and you really want to accept mail from such a sender, you can lower your spam filtering to the “Low” or “Off” setting.

It’s usually unwise to lower the filtering for your primary e-mail address, though. A better solution is to create a separate obscure forwarding address with the spam filtering lowered, then tell that sender to send to the special address.

For example, you could create this forwarding address in our “My Account” control panel:

secret.low.filtering@example.com  ->  address@example.com

Set the “Spam Filter” level to “Low” for this new address, then ask the sender to send messages there. This will work because our servers will accept even “forged” mail at this address.

Note that you should not change the spam filtering level for the target “address@example.com” address; doing so is not necessary and would cause you to get lots of spam there.

And of course, don’t tell anyone but the troublesome sender the new “secret.low.filtering@example.com" address address. If you use it elsewhere and spammers find out about it, you'll get lots of spam through it.

Can’t I just “whitelist” the sending address?

Unfortunately, that doesn’t work because the “invalid hostname” rejection is processed by our mail server software before the whitelisting system ever sees the address. Lowering the spam filtering is the only option for this unusual situation.