Setup client's Craft CMS site to use SendGrid for SMTP email sending
Go to the Google Admin console and create a group. I name the group like:
SendGrid: Client Name
And create the email address:
Then hit Create. Add any email addresses you want to receive mail to the group. Make sure the public can send message to the group using Posting Permissions: Public. Then send the invite from SendGrid.
When the invite arrives, I use 'clientname' as the first name, '@theportman.co' as the last name, then the above email address and set a password.
To setup sending with Craft CMS:
Host name: smtp.sendgrid.net