Last updated: July 2026

In short: At checkdomain you enable DKIM (together with SPF) with a single switch — provided you use the checkdomain mail server.

Prerequisites

  • A domain at checkdomain with active checkdomain nameservers
  • The checkdomain mail server via a web hosting package or the website builder (condition for the switch)

What is DKIM?

DKIM (DomainKeys Identified Mail) adds a digital signature to email, with which receiving mail servers can check whether the email actually matches the domain and wasn’t altered in transit. checkdomain summarizes SPF and DKIM as “methods used to better secure a domain’s email sending”.

For context: while SPF authorizes the server, DKIM secures the message. Only with DMARC does it become an enforceable foundation.

The starting point at checkdomain

checkdomain makes it convenient: one switch enables SPF and DKIM together. Unlike the plain SPF entry (which you can also set manually as TXT), DKIM activation runs exclusively through this function.

The decisive condition is in the fine print: the switch only works if you use the checkdomain mail server via a web hosting package or the website builder. If your mail sending runs via an external service (your own server, Microsoft 365, newsletter tool), this function doesn’t apply — then you publish your service’s DKIM key yourself as a TXT record (checkdomain supports TXT entries in the pro settings; the service supplies the key).

Step-by-step guide

1. Open the customer area

Open www.checkdomain.de, click My Login at the top right and choose Customer area. Log in with your customer number or email address.

2. Navigate to the domain

In the left navigation, click Domains, select your domain, and click Configuration.

3. Open Checkdomain Nameserver

On the domain’s detail page, click the Checkdomain Nameserver menu item.

4. Enable SPF & DKIM

Under Emails → Security, set the selection to Active and click Save. This enables SPF and DKIM for the domain.

5. Wait until the change is live

As usual at checkdomain: the value is saved in seconds, but worldwide visibility can take up to 48 hours.

The external case: DKIM without the checkdomain mail server

If you don’t send via checkdomain but via an external service, get the selector and public key there and enter them in the Pro settings of the Checkdomain nameservers as a DNS entry:

  • Hostname: selector._domainkey (dictated by the service)
  • Type: TXT (or CNAME, if the service — like Microsoft 365 — requires a delegation)
  • Value: the key supplied by the service

For Microsoft 365, see the two CNAME selectors.

Verify the result

Check your configuration with the free MXAudit scanner — it shows you DKIM, SPF, and DMARC at a glance.

Common mistakes

Expected the switch, but mail runs externally. The SPF/DKIM function only applies to the checkdomain mail server (web hosting/builder). For external sending you have to enter the DKIM key manually as TXT/CNAME.

Forgot the external service’s DKIM key. The switch only signs checkdomain mail. A newsletter tool or Microsoft 365 needs its own DKIM entry.

Wrong selector. For the manual entry, the hostname must be named exactly selector._domainkey, with the service’s selector.

Further reading