Description of the problem
Office 365 SMTP does not work with Open Bee™ Portal.
Solution
Install a local SMTP relay using IIS as described in this documentation: https://support.office.com/fr-fr/article/comment-configurer-iis-pour-le-relais-avec-office-365-eb57abd2-3859-4e79-b721-2ed1f0f579c9
Then configure portal to use this relay for sending (relay IP instead of Office365 IP)
Update: Version 6.10 of Open Bee™ Portal will allow direct connection to Office 365