Confusing Mailspring with Gmail/Office365 interaction

I’m in a bit of a peculiar state, but I think I’ve found a bug or sorts in Mailspring.

We’re currently in the middle of a migration from Gmail to MS Office 365. I’ve migrated the mailboxes to a temporary domain within O365, however, my actual user in both systems is @. So when I’m trying to setup Mailspring as a client for O365, it does a seemingly correct OAUTH procedure, but it’s using the wrong server for that:

rawLog: '----------IMAP----------\n' +
    'connect <mailcore::IMAPSession:0x7ffc570b4680>\r\n' +
    '* OK Gimap ready for requests from m26mb125211157ivt\r\n' +
    'ssl connect 993 2\r\n' +
    'OpenSSL version: OpenSSL 1.1.0f  25 May 2017\r\n' +

As one can see from the above debug log, Mailspring tries to login to GMAIL instead of O365. I’m guessing it’s because my MX record is still pointing to Gmail, but I’d say that is wrong, and it shouldn’t be affected by this as I’m setting up the O365 specifically, and even going through Microsoft’s OAUTH session in the browser.

I’m on Arch Linux, Mailspring version is 1.10.5-1ce06f18.

I would appreciate any hints.