Some DNS providers restrict the number of characters that can be placed into a TXT record. You can use the Email Deliverability feature in the cPanel interface to split the suggested DKIM record into 255-character parts.
1. Log into cPanel.
2. In the Email section, click Email Deliverability.
3. Click Manage to the far right of your domain.
4. In the section Suggested “DKIM” (TXT) Record, next to the View option, select Split.
5. Click the Copy button to copy the split record to your clipboard.