Tried it with one of our customer and no luck, have synchronization problems.

After the initial account synchronization in Outook, the sync stopped working. Tried the same account with Outlook 2019 and all working well.

I will investigate further by trying it myself... by installing 2021 version on a test computer and test MAPI it with my personal account.

Any further info on this?

I have 3 accounts using MAPI with no issues in Outlook 2021. 

We have many Outlook 2021, all working fine

Tested with my own account and all is working very well. Probably a glitch in the computer of our customer.

Hello, 

Thank you for posting your question here. We use Outlook 365 here for almost all of our testing. It works fine with SmarterMail. I don't see why Outlook 2021 wouldn't work as it looks like they are basically the same thing but 365 has more features. If you continue to have issues with Outlook 2021 feel free to submit a ticket and we can help you look into this issue further. 

Thank you,