Microsoft Office 365 users may be experiencing sending and receiving emails. Microsoft are aware and have released the following info
Title: Users experiencing delays sending email messages via any Exchange Online connection method
User Impact: Users may experience delays of over an hour when sending email messages via any Exchange Online connection method.
Current status: We’ve found the corrupted rules and are currently working to fix them. Once the rules are fixed, we will build a new deployment to remediate the problem.
Scope of impact: This issue may affect any user attempting to send email via Exchange Online.