Configuring preferences and options in Outlook.com
For me, all I care about is if I am going to lose old emails of which there are thousands. Or will it just be the attachments from them.
Old email will remain in your mailbox but to keep your mailbox under the (Microsoft Storage) 5 GB limit, you must delete email with large attachments. You can't delete just the attachments without deleting the emails they're attached to.
Also, I have in the past attempted to contact Microsoft directly, I know not to even bother.
I am an Exchange subscriber. Support responds very quick to my trouble tickets but they rarely help me solve my problems. 9 out of 10 I fix the problem myself and the other 1... they can't help me fix it.