DKIM uses cryptographic signatures and public-key infrastructure to verify that an email message has not been altered during transit, and that it truly came from the claimed sender. Email senders can use DKIM to sign their messages by adding a DKIM-Signature header field to the messages. Email receivers can then use the public key published in the DNS to verify the signature and check that the message has not been tampered with. 

SMTP2GO for DKIM: Why Should I Add Sender Domains?

It will be simpler for your recipients to recognize you if you enable Sender Domains for DKIM so that your email address can be changed to (sent from: yourdomain.com) rather than smtp2go.com. Additionally, you can enable DMARC so that any domains that send emails on your behalf must transmit authenticated emails that pass DMARC alignment, and your emails will be sent with DKIM signatures.

You can use Skysnag’s free DKIM Checker to check the health of your DKIM record here

Enable DMARC for your domains to protect against spoofing. Sign up for a free trial today!

For more information on SMTP2GO DKIM setup, you can refer to their reference documentation