To add a sender email using Mailmodo SMTP you need to first login to your account, then from your dashboard click on the 'Settings' tab from the left side of the window pane. Next click on 'Sender Settings' in the Settings section and in the 'Add New Sender' section add the sender address to be used as the sender name, then choose Mailmodo SMTP as the SMTP and click on 'Continue'.
After this a pop up will appear on the screen which will require you to get your email whitelisted by Google before it can render AMP emails in the user's mailboxes. You will need to fill this form and send it for approval. A step by step guide for the same is given here
Once you have sent the request for AMP email approval. You will be asked to add the records given below in your DNS. You need to copy the DNS settings displayed on your screen to your domain records. A step by step guide to add these DNS settings is given here
After adding the DNS settings in your domain, click on NOT_VERIFIED under Domain Authentication. If you have added the DNS settings correctly the status will change to 'VERIFIED'.
Your email address is now configured as a sender but will have to be registered for AMP to send AMP emails
Here's a short guide on dkim, dmarc and spf, and why are they important.