I have a large number of users who were unable to send emails after the April update to Outlook 365 was installed on their systems and I have not been able to find any relevant discussions on this topic here. They all use company owned Gmail accounts and connect to their gmail accounts in Outlook by using G Sync. Any emails they create and send go to the outbox but never get sent out and there are no sync error messages from GSync. I found a conversation with Google support reps that said they have received numerous support tickets regarding this issue and suggested a way to roll back the version of Outlook 365 to the previous monthly update and then disable further updates. I tried it out and the problem was immediately resolved on all of our current Windows 10 systems. However, when i install Office 365 on any new Windows 10 PC's, I am unable to roll back the update as no previous updates are installed and installing old updates manually is proving to be more difficult than anticipated. Is there an actual solution from MS out there for this issue?
I have had my fair share of emails stuck in outbox, though not in the specific context you mention.
I would classify them as "A Tale As Old As Time". There has never been a fix from MS in 20+ years, the only workaround I could ever use is to just delete all emails in the outbox, and recreate the emails to be resent. Crummy and unoptimal, but stuck emails also may block all further outgoing email .
Maybe there is something different to your case, as you mention specifically the G Suite connector and problems arising after an update.
But maybe the workaround above works in your case? If it doesn't, it will also be important to diagnose the issue.
I've tried clearing the outbox and sending new emails but they all end up stuck in the outbox. I tried building a new Windows 10 system without GSync and it can send emails, albeit slow at times. it depends on how much syncing it has to do. One test email took an hour to send, the other was instant. I've had issues in the past with Outlook mailbox syncs failing and getting stuck like that for PC's that weren't using GSync, which is why i try to always use GSync. I guess I'll have to cross my fingers and hope for the best for now