Exchange online forwarding

Question

Hi all,
I have a problem with email forwarding and I hope for your help.

Example:
myFirstAccount@example1.com --> is the mail mailbox that forwards the email to mySecondAccount@example2.com
mySecondAccount@example2.com --> is the mailbox that receives the email forwarded from the first mailbox
customer@example3.com --> is my customer's mailbox

If customer@example3.com sends an email to myFirstAccount@example1.com and mySecondAccount@example2.com is temporarily out of order, my customer receives a message from microsoftexchange@mydomain.onmicrosoft.com with the error "Delivery failed for the following recipients or groups: mySecondAccount@example2.com".

I don't want my customer to know that I'm forwarding my email to my second account.

Is possible to avoid this behavior?

Thank you for your help.
AS

Answer 1

Hi @Alain Sorrentini
Ok, thats a different the issue. You are forwarding and that breaks all the SPF/DMARC checks.

Office 365 has a mechanism to address this:
https://learn.microsoft.com/en-us/office365/troubleshoot/antispam/sender-rewriting-scheme

But, this is really on the other provider. If they are dropping this, you need to talk to them to see if you can whitelist these messages

Answer 2

Thanks for your explanation and your time.

Answer 3

There is no way to prevent NDRs per mailbox in that way. If there is a problem with any mailbox in your tenant. Exchange Online is going to report it to the sender.
Why is the forwarding to mailbox "out of order"?

Answer 4

In stead of forwarding, you could try with a mail flow rule (transport rule). You do that in Exchange Online.

The logic would be:
If a message is sent to myFirstAccount do the following
Add following recipients in the To-Address: mySecondAccount

In order to test if a NDR is generated, you would temporally need to invalidate the To-Address. Easiest way would be to add a second SMTP address to mySecondAccount.

First you test if the rule works, then you remove the secondary SMTP address and check if a NDR is generated to the original sender.

Answer 5

Thank you for your reply.

The message sent to my customer says:
mySecondAccount@example2.com
mxbw.lb.bluewin.ch
Remote Server returned '554 5.2.0 <mxbw.lb.bluewin.ch #5.2.0 smtp;554 5.2.0 sc971: SPF hard fail>'

Note: mySecondAccount@example2.com is managed by another provider (not Microsoft).

Thanks again
AS