Custom DKIM signatures

DKIM (DomainKeys Identified Mail) is a technique for digitally signing an email, so that a particular domain name can claim responsibility for that email.
DKIM-Signature: field is added to the email's header.

By default, SMTP2GO signs all emails with our own DKIM signature. This works fine in most situations, however some Gmail recipients may see that emails are being delivered "via". In addition, better email delivery to Hotmail/Yahoo/Gmail/AOL can be achieved by using a custom DKIM signature, and if you need to setup a DMARC record (which is useful to prevent spammers sending phishing emails from your domain name) then a custom DKIM signature is essential.

To setup a custom DKIM signature, follow the steps below:

Step One:

From the left-hand menu, make your way to the 'Settings > Custom DKIM' page in your SMTP2GO control panel.

On the screen, in the Your Domain field enter the domain name you would like to use in your DKIM signature. For example, if you send your emails from then you would enter

Enter any keyword into the Selector field. We suggest entering a keyword such as smtp2go.

If you wish to use this DKIM signature by default, ensure that the Use as Default box is checked.

Click Save Changes.

Once the changes have been saved, you will see a list of your Registered Domains. You can always add more here.




Step Two:

Login to the DNS administration of your domain name. This is often available through a web-based system such as Cpanel or Plesk. If you are unsure, please contact your IT or web administrator, and ask them how to update your DNS settings.

Create a TXT record in the DNS settings for your domain name, using the name and DKIM key that we provide you.

We have some setup guides for popular webhosts here.

If you are using BIND to edit your DNS, then you would create a single line entry, in this format: TXT "your dkim key"

How do I know it is working?

There are 3 ways that you can test:

1) You can test your DKIM signature by using the email testing service provided at IsNotSpam.

2) You can send a test email to your email address. Then login to your Gmail account, view the email and click the 'Show Details' arrow to display this information:



Additionally, you can click the down arrow next to 'Reply', then select 'Show Original'.

You will see the underlying code of the email. Look for dkim=pass and your domain name showing on the same line:



3) You can send a test email to your email address. Then login to your Yahoo account, view the email and click 'View Full Header' from the 'Actions' menu. Look for dkim=pass and your domain name showing on the same line.




I’m seeing an error with my DNS settings when trying to add the DKIM record. What can I do?


Some hosts do not support underscores (_) in DNS records, and adding the DKIM record can cause an error. The underscore is required and you’ll want to contact your host and see if they can manually add the record for you or if they disallow underscores entirely.

Semicolons (;)

Some hosts require that you escape semicolons in records. If you’re getting an error, try replacing ; with \; .

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