Emails were working fine on a 2.1.7 site but when I setup 2.2.1 and 2.2.2 sites I couldn't get transaction emails to work. Tried and tested everything. Installed the SendGrid extension as well and still nothing.
Note I had to manually set up cron jobs as they were not set up when I installed the stack on Azure.
In the end I upgraded GmailSmtpApp from v1.4.5 to v1.5.1 and transaction emails are now working. Tested with Gmail and SendGrid successfully.