Sender domains

SMTPeter uses the concept of "Sender Domains" to simplify email. At all services that Copernica offers, it is mandatory to use sender domains. This allows you to send your email through our servers without having to worry about complicated things like SPF, DKIM and DMARC. You focus on your business, while we take care of your messages.

But what exactly do we mean with a sender domain? It works pretty neat: you open the SMTPeter dashboard to specify from which domains you intend to send email, and we tell you how you should configure your DNS. The "sender domain" is the domain name that you are going to use for your mails.

For example, if you want to send out emails using addresses that end with "" or with "", you simply use the dashboard to set up two sender domains: "" and "". After you've set up these sender domains, SMTPeter gives you a list of recommended DNS records. You copy these records to your DNS server (or give them to your DNS provider) and that's basically all there is to it: after you've followed our recommendations you can use SMTPeter to send email.

A little more details

Lets be honest here. Sending email is getting more and more complicated. There are a lot of things to care about: you have to set up SPF records in your DNS in which you list all IP addresses from which you send out email, you need rotating public/private key pairs for DKIM signatures, and you also want to set up DMARC records in your DNS so that the world knows that you are the only one who uses your domain to send mail.

With "sender domains" SMTPeter takes all these responsibilities out of your hands. We create your SPF, DKIM and DMARC records and store them on our DNS servers. All that you have to do is create a couple of records in your DNS record (or ask/instruct your DNS provider to do so) pointing
to our records. If we make a change to the DNS (for example, because we rotate one of your private DKIM keys), it gets automatically propagated over the internet, because your DNS records just point to our records.

In our DNS (using * subdomains) we set up the following records:

  • SPF records that list all IP addresses from which you send email
  • DKIM keys with your public keys that we rotate once a month
  • DMARC records with your DMARC policies

We ask you to set up CNAME records and other aliases in your DNS to refer to these records.

The "from" address

For each sender domain we host the public DKIM keys in our DNS. We also have a copy of the private key on our servers so that we can add a DKIM signature to each mail that flows through the SMTPeter servers.

To decide which keys to use, we extract the "from" address from all emails that we process. That's why it is important that you always use the same domain names in the from addresses of your emails. Only the emails for which you've set up a sender domain can be signed.

The tracking and bounce domains

If you set up a sender domain you are asked to configure your tracking and bounce domains. These are the hostnames that we use to track clicks, opens and errors. The suggested defaults, "" and "" are sufficient for most users.

Please be aware, however, that if you configure SMTPeter to track clicks all hyperlinks in your emails are going to be rewritten to use the click domain. The default "" might look like a tracking domain to your users (which is not that strange, given the fact that it actually is a tracking domain). If you rather have URLs that look more neutral (for example "", or "") you can change the click domain in the sender domain configuration.

The same applies to the bounce domain, although the bounce domain is less visible for the receivers of your email. It is only used for the envelope domain, which is normally not shown to users, unless they inspect the original email source.

More information

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You can find this documentation page on GitHub.
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