Is Thunderbird MAPI compatible?

You did not fully explain what you need. Here is a nice summary of the topic:

https://www.cleverence.com/articles/sage-documentation/mapi-compliant-7294/  this article may help: 
https://kb.mozillazine.org/MAPI_Support 

Maybe, if you describe what you actually need, we can provide better assistance. Thank you.

David - Thanks for the response. I am trying to send emails with Word Mailmerge; it isn't working (as I am using it anyway) and when I go to "Help"n one of the first things it says is that I need a "MAPI-compatible" email. I don't know what else I can tell you. Regards - Karl Sovik

Here is what I found in AI:

MAPI Compliance in Thunderbird Overview of MAPI Support

   MAPI Compliance: Yes, Thunderbird is MAPI-compliant, which means it can interact with applications that utilize the MAPI protocol.
   Supported Version: Thunderbird specifically supports SimpleMAPI, allowing basic email functionalities with compatible applications.

Extended MAPI Support

   Extended MAPI: Thunderbird does not support Extended MAPI, which is a more complex version of the protocol used primarily by Microsoft Outlook.
   Implications: This limitation means that while Thunderbird can work with many applications using SimpleMAPI, it may not function seamlessly with those that require Extended MAPI features.

I hope that helps you. Good luck.

Thanks!

You are very welcome. I hope this helps.

See also https://kb.mozillazine.org/MAPI_Support