First visit Dashboard -> Settings -> ActiveCampaign Postmark and click on the Logs tab to see if there are any errors. If this settings page doesn't exist, check that the Postmark plugin is active and configured.
The email address no-reply@canplanmail.com can be used in a pinch if we have not yet set up an approved sending domain for the client. Put that email in the Sender Email box and let Kory know we need to set up Postmark for the client.
Common Postmark error messages below:
ErrorCode: 400
Message: The 'From' address you supplied is not a Sender Signature on your account. Please add and confirm this address in order to be able to use it in the 'From' field of your messages.
Solution
a) on the ActiveCampaign Postmark settings page check the "Force Sender Email" box, this will force the website to send emails from the approved domain in the Sender Email box.
and/or
b) Make sure the Gravity Form "from" address matches the approved domain in the Sender Email box