Guide per DNS host

Set up DKIM at netcup

DKIM signs outgoing mail with a key whose public part lives in DNS. At netcup the key is generated in the control panel; if the name servers are at netcup too, the DNS record is usually set automatically. This guide shows both steps and the mistakes that invalidate the signature.

Enable DKIM at netcup

In the web hosting panel (Plesk) enable DKIM for the domain under "Mail" → "Mail settings"; with netcup name servers the records are added.

SPF: v=spf1 mx ~all is common with netcup web hosting when only the netcup servers send.

Other senders sign separately

Every service sending on behalf of the domain needs its own DKIM key with its own selector: the newsletter tool, the CRM, Microsoft 365. The records do not interfere because each lives under a different selector. DMARC then covers all of them.

How to add the DKIM record at netcup

The way to the netcup DNS editor:

  • In the netcup Customer Control Panel (CCP) open "Domains" and select the domain.
  • Switch to the "DNS" tab and choose "Add new record".
  • Type and name as shown by the mail provider: usually CNAME or TXT under selector._domainkey. The selector name goes before _domainkey, the host appends the rest of the domain.
  • Enter host (@ for the apex), type and destination, then "Save DNS records".

Typical mistakes at netcup

  • Selector missing or misspelled in the name, so the receiver finds no key.
  • TXT value truncated for long keys or split into several records.
  • CNAME next to other records on the same name.
  • DKIM enabled in the control panel but the name servers are elsewhere and the record is missing there.

Verify and keep an eye on it

After saving, the change at netcup usually applies within minutes. The checker below queries the authoritative name servers and shows right away whether the DKIM record is read correctly. DomainWarn keeps checking the record afterwards and alerts you when it changes or disappears, for example after a migration or one click too many in the DNS editor.

Frequently asked questions

Why does the checker find no DKIM record after enabling it at netcup?
Either the name servers are not at netcup and the record is missing there, or the selector differs from the common ones. Enter the selector name from the netcup control panel in the DKIM checker.
Which key length is right?
2048 bits. 1024 bits is considered too short, longer keys do not fit every DNS editor.
Check now

Free DKIM record check and lookup: selector, key type, key length, syntax and revoked keys. Leave the selector empty to try common selectors automatically.

Selector is optional: leave it empty to check common selectors automatically.

DomainWarn checks SPF, DKIM, DMARC, DNS and certificates of all client domains regularly and reports changes before mail lands in spam.

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The same guide for other hosts