I have no idea what "Outlook Microsoft Graph REST API" even is. I am that disinterested in Microsoft and paying someone for email. I do understand that there are moves afoot to use some Microsoft proprietary protocol with exchange which is what office365 is. See https://blog.thunderbird.net/2024/04/adventures-in-rust-bringing-exchange-support-to-thunderbird/ Sure tht announcement is almost a year old, but I understand elements of it are now in daily developer builds as these discussions would suggest. https://thunderbird.topicbox.com/groups/daily how far from release, I have no idea. But as ESW is still good for another year I don't think there is a rush yet.