I'm on CiviCRM 5.9 on WordPress. We just did our first batch of year-end contribution summary letters, and ran into an issue when choosing the "Send emails where possible. Generate printable PDFs for contacts who cannot receive email" option. We have a total of about 550 letters/emails to send.
We're using G Suite as the SMTP server, and in looking at the logs, it looks like Google started rejecting the emails after about 100 or so had been sent. The resultant PDF of letters wound up with about 450 pages, including many contacts who do have email addresses (and therefore should have been sent an email).
Since this is my first time doing this and we don't send out any other bulk emails, I took at look at the CiviMail settings and they're all set to the defaults (0 across the board), which is I assume what caused the issue. But I wasn't sure if the specific "Thank You Letters" function actually used those settings or not.
For reference here's the error message in the logs:
Jan 31 15:29:08 [info] Ignoring exception thrown by nullHandler: 10004, Failed to set sender: EMAIL_ADDRESS_HERE [SMTP: Invalid response code received from SMTP server while sending email. This is often caused by a misconfiguration in Outbound Email settings. Please verify the settings at Administer CiviCRM >> Global Settings >> Outbound Email (SMTP). (code: 421, response: 4.7.0 Try again later, closing connection. (MAIL) z7sm8172274pga.6 - gsmtp)]
I verified the settings are correct, and I can send test emails from the settings page fine, but my guess is I triggered a block on the Google side, so I wanted to make sure that if I update the settings and try again that those actually apply to this particular task.
As for the actual settings for Google, I came across these: Questions About Mailer Settings - Suggested G Suite settings?
Are those good settings? Anyone else using G Suite as SMTP have any other advice on settings, particularly as relates to sending out Thank You letters?