DKIM Setup for Gandi
Create the Custom DKIM Signature as per the instructions here.
Log in to your Gandi account.
Click on the DNS Zones tab. Select your appropriate domain and create a new version of your DNS Zone.
Click the Add button under Zone file versions.
Select the TXT from the Type drop-down menu.
Enter selector._domainkey (replace selector with your selector) into the Name field. If your selector is smtp2go, then it is smtp2go._domainkey.
Paste the DKIM Signature, which is created at Step 1 into the Value field.
Click the Submit button.