Outlook Add-on in MS Marketplace not allowing install


I am trying to install the Asana for Outlook addon via the MS Marketplace and getting the following error when clicking “Get it now” from my business email address :
Installation failed
REST API is not yet supported for this mailbox

Does anyone know why this is occuring?


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@thomas.livesey I would suggest checking with you companies Outlook admin as I believe you have to allow third party add-ons to be available. I know in my case, my client doesn’t allow third party add-on without extensive due process and justification…


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Dear all,

I have encountered this issue as well: “Installation failed, REST API is not yet supported for this mailbox”. At our company we use all kinds of Microsoft Office versions. We tried it on 2010, 2013, 2016 and 2019 versions and none of them worked. One colleague had Office 365 and he had installed the add-in without any issues.

Could somebody guide through this problem, since our company’s IT support has no clue on this issue so far.