Office 365 e-mail service is down for some users around the world. Microsoft confirmed the issue and mentioned that some Office 365 users can’t access their mailboxes through multiple protocols. After investigation, Microsoft has now found the cause of this issue. A subset of Domain Controller infrastructure became unresponsive, resulting in user connection time outs. Microsoft is already applying steps to mitigate the issue. If you are one of the users who got affected, try accessing the mailbox again after sometime. Everything should work as expected!