Hey Kim,
Yeah, that was my first thought, but we verified that the addresses existed as aliases already, AND that the sendas command worked for other aliases configured the same way for the same user.
I think what happened was this:
- New account that had a lot of legacy data migrated from M365.
- The sendas command has an API flag to retroactively apply the sent label to all messages with the new sendas as a from address.
- Normally, this isn't a lot of mail and it can loop through any existing messages pretty quickly and apply the label.
- Because this was migrated, there were thousands of messages that needed to have the sent label applied, so it timed out on that piece.
- Google appears to have now rolled out a fix that allows this to complete without erroring out.