Created a login at walmart.com with passmail alias

Created an order and got an error message that said to contact accountreview@customercare.walmart.com

I clicked on it, it brought up a PM email with one of my PM aliases in the From field.

Since the domain name I'm sending to doesn't match the one in Pass, I wanted to change 'From' address to the passmail alias. But I can't.

I like PM and it's my primary email now, but Thunderbird's ability to change the From address would be good here.