Troubleshooting Exchange Inbox Rules and Missing Emails in Office 365

Emails Not Delivering to My Inbox

Nothing is more frustrating than expecting an email and finding that it’s nowhere to be seen, even when your correspondent is adamant they sent it to you.

Usually, after you’ve checked the obvious things like misspellings, the problem is mailbox filtering rules.

What Are Mail Flow Rules and Inbox Rules?

Most of our clients use Office 365 for their email services. The email component of Office 365 is called Exchange Online.

It’s possible (with Office 365 and many other email systems) to put rules in place to pre-handle certain types of email before they reach your inbox. This might be flagging certain emails as junk, or you can use rules to auto-forward emails to certain departments, or file them into folders.

In Exchange Online, users can set their own “Inbox and Sweep rules” independently. These are applied when a message reaches their inbox. Administrators can also set Mail Flow rules in the Exchange Admin Center, these rules are applied before anything gets delivered to the user’s inbox.

What Can Go Wrong With Inbox Rules?

As you can probably tell, Inbox Rules and Mail Flow Rules can prevent emails being delivered. They might be redirecting the email elsewhere, or they could be rejecting it as junk mail without you realising.

We have seen a few cases lately in Exchange Online where some ‘hidden’ rules get applied to a user’s mailbox and this causes email non-delivery when all other possibilities have been eliminated.

Diagnosing Email Flow Problems

1. Ask an administrator of your Office 365 account to run a Message Trace in the Exchange Admin Center. It will tell you if any emails were intercepted by rules, and for what reason.
   • This serves two purposes:
     • Firstly, if the message trace has detected the missing email, you know it reached your email system and therefore something within your control prevented it being delivered
     • Secondly. the message trace will say why it was rejected; often it will indicate that rules on the mailbox caused a rejection or other behaviour
2. If a message trace indicates the message reached your email system, ask your administrator to check your Mail Flow rules to see if something caused it to be rejected or redirected
3. If there are no Mail Flow rules causing the problem, check your own mailbox rules in Outlook Webmail 
   • Click the cog wheel > View all Outlook settings > Email > Rules
   • Tip: you can turn them off without deleting them if you need to troubleshoot email mis-delivery, then reenable when finished
4. If there is no obvious cause in the mail rules, you may have a common problem with hidden rules on your mailbox

Fixing Hidden Mailbox Rules in Exchange Online / Office 365

If your message trace indicates that mail rules caused an email to not be delivered, but you cannot find any relevant rules in your settings, you may have an issue with hidden rules. This is fairly common in Exchange Online (Office 365). You will need to ask your administrator to help with this.

• Start by logging into Outlook Webmail 
• Click the cog wheel > View all Outlook settings > Email > Rules
• Click the link to generate a diagnostic report which will be delivered to your inbox
• Locate this email and send the attachment called “InboxRules.txt” to your administrator

Your administrator will need to:

• Scroll through the InboxRules.txt file and identify any lines which say “Index=Y” where Y is a sequential number.
  • Each of these entries identifies a rule on your mailbox, which may not have been visible before
  • Take a note of each rule’s “ID” number, which is two lines down from each sequential ID and is a long random number
• Open a PowerShell session to Office 365 / Exchange Online per these instructions
• Use the Remove-InboxRule PowerShell command per these instructions and use the ID noted above – not the Index number –  to identify which rule(s) you want to remove
  • We usually recommend deleting all rules and starting afresh
  • Example command:   Remove-InboxRule -Mailbox Joe@Contoso.com -Identity “4354517577245”

Run another diagnostic report and the InboxRules.txt file should be empty.

You may now be able to receive your missing email normally and you can proceed to reinstate your old rules.