Hello, 

Thanks for reaching out to the community. This is interesting I just tested this and it worked for me. Make sure that you're allowing less secure apps. 

Kind Regards, 

It looks like the error occurs when you try to import contacts or check anything other than the email. Yes, less secure app access was on. FYI that is ending soon though!

This is a known issue. The Google API's used by SmarterMail for migration are considered secure by Google and require additional checks on their side in order to fully unlock access to them. You can check out this blog post for more details:

Due to these security restrictions, the API key used by SmarterMail is restricted to connecting to a limited number of accounts. Unfortunately, this is a lifetime restriction, so removing permissions from a connected account does not free up a spot for another account to connect.

The upcoming beta will include a way to work around this limitation.

Even with allowing "Less Secure App turned On" and the statement that after May 30 2022 this will no longer be allowed, I'm setting being blocked from migration. Nice

EDBMails is now NOT RECOMMENDED. It now does not perform as it should, with folders marked for migration missed entirely in the target account, and some folders logged as migrated (with correct message counts) but target folders are empty.

I have left the following in place, but my review summary for EDBMails has changed to STRONGLY NOT RECOMMENDED.

Another shameless plug, this time for a migration product (I get nothing for reporting this, have no financial interest in the product): I got tired of trying to get support from Bittitan while Microsoft changed the back-end rules, and needed to make appointments with Transend to try and get support. This is a breeze by comparison, support-wise. The pricing is super-attractive. And it works. So here goes...

I have successfully used EDBmails (edbmails.com) to migrate users between servers. Haven't used it with gmail but have used it for IMAP on SmarterMail and iMail mailboxes --> Microsoft 365. Really cheap per user and excellent 24x7 live chat support, which is free with the product. 

Definitely a bit of a learning curve but once in operation, it's been bulletproof in terms of what it migrates. Windows app, can be installed on multiple computers and run simultaneously. You pay per user. For example, 100 users is currently $200 ($2/ea.) - more per user when you buy fewer licenses - and can do as many full/incremental migrations as you like per user. Lifetime license for each user migrated, and free upgrades. Also migrates IMAP to pst files. 

You also get a good idea of progress during migration, something I've found lacking elsewhere.

Other migration types/products listed on their site.

BTW this is NOT a dig at SmarterMail, as all environments I've migrated have kept their on-premises server in a split-domain arrangement with Microsoft 365. Migrations were done in accordance with customer requirements for some users.

Never used edbmails.com, but imapsync (local app) has worked for us perfectly. We did one migration a few years ago with over 4000 accounts and it worked flawlessly, but it only does emails which can be a problem for some.

Just to clarify, the tool worked fine when we just imported emails and NOT emails + Contacts. It will not allow contacts to be imported.

Migrating accounts to M365 is more "interesting" these days because of Microsoft tightening up security at the back-end, and, FAICT, constant changes back there as well.