External meeting request cannot be forwarded internally because Office 365 Exchange sees it as coming FROM the original external sender

External meeting requests cannot be forwarded to internal recipients because Office 365 Exchange sees the message as coming FROM the original external sender, not the internal sender actually sending the message.  We use a 3rd party email filtering service and have setup a Rule in Office 365 Exchange that prohibits the delivery of any email that does not come "FROM" the IP address of the 3rd party filter.  The message will fail with a 5.7.1 error.

Does anyone know of a way to alter the RULE in Office 365 Exchange so that it will make an exception when an internal user is forwarding a meeting request that originally came from an external sender?  I know this may be confusing.  Please let me know if you need any clarification.
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Go into exchange online admin center.  Setup a custom mail rule.  I've never had a need I wasn't able to configure there.

Have you already looked there?
griffisblessingAuthor Commented:
ScriptAddict - thanks for the suggestion. I do currently have a rule and it's 99% OK.  The issue here is arising only when someone forwards a meeting request that originally came in from an outside email address.  This is because Exchange sends the forwarded message as being from the external sender, even though it's being forwarded by an internal user.

At any rate, what I'll be trying next (need to wait for a low traffic time because this is a production environment) is to turn off the existing Rule and enable a new Connector that I've setup for incoming email.  The thought here is that the Connector is closer to the Internet and won't be as sensitive this "internal" forwarding issue.

I will post back as to whether this worked or not once I have implemented and tested it.

Thank you.
griffisblessingAuthor Commented:
UPDATE - disabling the Mail Flow Rule and enabling/creating a new Connector for our filtering "partner organization" seems to be having a positive result.  Mail inflow and connector reports in Office 365 are now reflecting that the vast majority of incoming messages are now coming in only through the new Connector.

That being said ... I've read all kinds of articles over the past few days in trying to figure this out.  It seems that Microsoft keeps changing things in Office 365, so it's a bit of a moving target.  Most of what I read recommended that BOTH a Connecter and Mail Flow Rule be created in order to have the most secure environment.  This is great - and I agree - except for the fact that the Mail Flow Rule was blocking the internal forwarding of meeting requests originally received from outside senders.  Ugh, it's been a real cluster.  I'm not sure why Microsoft can't make a more obvious overarching setting that controls inbound email from the Internet.
griffisblessingAuthor Commented:
^^^ see above

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