Emails to a mailbox mysteriously being forwarded

Question

Emails to a mailbox mysteriously being forwarded

-- -- 957

Hi

We have Outlook desktop clients connected with Exchange 365 backend.

We have a very peculiar issue that all email to one mailbox is being forwarded to an external contact and we can't find out why. The forwarded emails have a FW: in subject and are saved in Sent Items of the sending mailbox so its probably not being done by Exchange rather one of the Outlook clients? I did check in Exchange and there is no forwarding rule when using;

Get-Mailbox -ResultSize Unlimited -Filter "ForwardingAddress -like '*' -or ForwardingSmtpAddress -like '*'" | Select-Object Name,ForwardingAddress,ForwardingSmtpAddress

We have also checked Outlook clients and have not been able to find any rule that does the forwarding.

Any clues as to where should I look for this forwarding?

Thanks

Regards

AlexC 246 Reputation points

2021-05-03T19:18:03.217+00:00

Hi 7,
do you already know, which mailbox is forwarding those e-mails?
If yes, did you check with Get-InboxRule cmdlet?

I'd suggest blocking forwarding using a transport rule as described here:
https://techcommunity.microsoft.com/t5/exchange-team-blog/the-many-ways-to-block-automatic-email-forwarding-in-exchange/ba-p/607579

KR, Alex

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AlexC 246 Reputation points

2021-05-03T19:18:03.217+00:00

Hi 7,
do you already know, which mailbox is forwarding those e-mails?
If yes, did you check with Get-InboxRule cmdlet?

I'd suggest blocking forwarding using a transport rule as described here:
https://techcommunity.microsoft.com/t5/exchange-team-blog/the-many-ways-to-block-automatic-email-forwarding-in-exchange/ba-p/607579

KR, Alex

Answer 1

Jade Liang-MSFT 9,986 Microsoft Employee

Hi @-- -- ，

As far as I know, in the Outlook client, apart from rules, there may be no other options to set up automatic mail forwarding. In order to further avoid the interference of rules, it is recommended to temporarily turn off all rules in Outlook to check if the issue has any differences after that.

If the issue still exists, I think it may be related to your account itself, as I know, for Microsoft 365 account, we could also forward message automatically via owa, it's suggested to check your setting like below(settings>view all Outlook settings>Mail>Forwarding)

If your issue has any update, please feel free to post back.

If the response is helpful, please click "Accept Answer" and upvote it.
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Jade Liang-MSFT 9,986 Reputation points Microsoft Employee

2021-05-07T09:31:35.85+00:00

Hi @-- -- ,

Does this issue have any updates? If it has been resolved, please click "Accept as answer" to mark useful post or share your solution, your action would benefit others who have similar issues. If you have any questions or need further assistance, please feel free to post back. Thanks!
-- -- 957 Reputation points

2021-05-07T17:34:04.207+00:00

Hi

So issue is unresolved and MS O365 support suggested that I use MFCMAPI to check that there isn't a corrupt rule hiding somewhere. I tried MFCMAPI on the main pc used by that user and it did not find any hidden/corrupt rules. For now I have added a rule in Exchange to block the forwarding.

Thanks

Regards
Jade Liang-MSFT 9,986 Reputation points Microsoft Employee

2021-05-11T09:53:53.327+00:00

Hi,

Thanks for your update.

If you are still researching for it, as I know, we could clear all rules in Outlook and server via "Outlook.exe /cleanrules" Command Line Switches, in order to confirm if the issue is related to your rules, we could try to first export all rules and clear your rules for testing.

Hope that would be helpful to you.
Jade Liang-MSFT 9,986 Reputation points Microsoft Employee

2021-05-14T04:46:29.707+00:00

Hi,

Just checking if your issue has any update, if so , please feel free to post back :)

Answer 2

Ken Kam Hung, Lin 91

Hi @-- -- ,

Do you know that account has access to outlook 365 too? if so, you may try to run the same powershell in the following link to check all forward rules that belongs to that user.

https://gcits.com/knowledge-base/find-inbox-rules-forward-mail-externally-office-365-powershell/

Regards,
Ken Lin

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Emails to a mailbox mysteriously being forwarded

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