I do have a really weird one. I am running a webhosting server that is being blocked by certain providers that use Cloudmark. I contacted the customer support and they got back with an email header that is unfortunately sending spam.

Received: from sub.domain.example ([ servers ip)])
Subject: sven.n.nilsson,=?utf-8?q?=62=65=6b=72=c3=a4=66=74=61=20=64=69=74=74=20=64=65=6c=74=61=67=61=6e=64=65=2e=2e=21=21=21?=
From: =?utf-8?q?=53=77=65=64=69=73=68=20=6d=65=74=68=6f=64?=  <VNH9DI6HOW68YGD4AWRMSPB0VT7UWSHX5@gmail.com>

The header states, that the mail came from my server. But how is that possible, I do have a closed relay and there is no mailbox for that domain. Furthermore, the domain is pointing to my servers' IP. How can I prevent it from faking email headers and pointing to my servers' IP?

  • You say a webhosting server. Are the only accounts on the server yours? – Steve Dec 8 '19 at 1:45
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    Check the files on your server, maybe someone uploaded a file that is allowing attackers to send emails from your server. Also you should be able to prevent it by setting correct SPF records on your domain – NatWeb Solutions Dec 8 '19 at 5:29
  • Thanks. Will check that. – Andreas Schantl Dec 8 '19 at 19:04
  • And yes. It's only my accounts. But I'll definitely have look at the files if I can find anything suspicious – Andreas Schantl Dec 8 '19 at 19:05

First of all,

You would have a security breach, so please check your server or hosting account for security-related problems and then to mitigate the sending of spam emails (spoofed) from that domain(subdomain) create a TXT record (DNS) with the following.

sub.domain.example TXT "v=spf1 -all"

By doing this you're telling the whole internet that this subdomain is not intended to send mail, please do this even if you don't have a mailbox in your server.

| improve this answer | |
  • How do you know it is a security breach? – Steve Aug 25 at 6:45
  • He stated that the header of the sending email was coming from his server ip. – Santiago Aug 25 at 12:22
  • That doesn't necessarily mean a "security breach" unless you mean it in the most broad of terms. – Steve Aug 25 at 21:40

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