fyr.io

TL;DR: You're logging in using a non-primary alias for the account. Use the primary alias and your email will migrate smoothly.

We're migrating around 100 email accounts that were on Exchange over to Google. This has involved changing some peoples alias so that they match up with everyone elses (<initials>.<id>@<domain>) however we've added their old address as an alias so they can still receive emails sent to their old address (eg: <fullname>@<domain>).

Due to some political reasons we're unable to touch the exchange server, so we're using the G Suite Migration for Microsoft Outlook tool. It's been fine up until today where we started seeing the following:

Note the Emails - they are all failing! What was odd was that this was only happening for one of the techs. He must have been doing something wrong! We monitored their steps and it all looked fine though. Taking a look into the trace file we could see the error appearing as Failed with 0x8004106b. Googling this didn't result in any usable results, but as we were looking into it another tech appeared and just happen to glance at the screen as the original tech was attempting to migrate a user again. Our spreadsheet contained some info including the primary email address and the alias for us to check and the tech noticed that the guy with the sync issues on his users was using the non-primary alias to log in. After trying the primary alias, the emails migrated successfully.

Interestingly, the Contacts and Calendar data synced correctly.