Resolved -
Here's what was done:
Deleted 1 of the 4 WHD incoming email accounts and worked through the KB article for configuring OAuth from scratch with the primary incoming account to satisfy the tech - confirmed the original problem still existed
Updated to a 12.8.3 hotfix instead of the current version because the WHD dev team told them that specific build might have the problem fixed, but got broken again in the current 12.8.4 build - confirmed the original problem still existed
Updated to 12.8.4 because somebody on the dev team remembered that 12.8.3 hotfix 3 has a problem that slows WHD to a crawl in production - confirmed the original problem still existed
Switched to using IMAP basic authentication instead of OAuth using a Google App Password configured on the email service account's Google account, which requires enabling 2-factor authentication in the Google account, backing out of the 2-factor authentication screen and then clicking back into it to discover that a new "App Passwords" configuration button has magically appeared, clicked it, created an App label (I used "WHD") and then copied and pasted the 16-digit auto-generated password into the WHD account password field, checking the SSL box, then clicked Save to commit.
Watched the connection time out and display an error in the email config interface.
Stared blankly for a while.
Realized that there is a firewall allowing POP traffic outbound and inbound for the WHD server, but not IMAP; added IMAPS and SMTPS to the policy.
Went back to the WHD email config and tried the connection again. Connection went green but there was still an error about there being messages in the Inbox. The error dialog instructs to click the "Commit Settings" button that has magically appeared at the bottom of the configuration screen.
Checked the email history interface, waited for the history screen to update and verified tickets are now processing.
Repeated the 2-factor enablement and other necessary steps for the other 3 accounts, verified ticket processing is functional.
-Josh
Mar 27, 18:58 PDT
Update -
We are continuing to investigate this issue.
Mar 27, 09:29 PDT
Investigating -
It has come to our attention that our Web Help Desk email forwarding service is currently not functioning properly. This means that any responses to tickets sent via email won't update tickets, and thus our technicians will be unaware of your response. Please only respond to tickets through the help.eusd.org portal while we're working to fix this issue. We apologize for this temporary inconvenience.
Mar 27, 09:28 PDT