Hi all,
Version 8.6 has now reached public beta, which includes OAuth2 Support for Microsoft Email Services, for both sending and importing: https://blog.whmcs.com/133721/whmcs-86-beta-now-available

Please join us during the pre-release testing period and provide your feedback in our dedicated beta community board: https://whmcs.community/forum/590-whmcs-86-beta-discussion/