Multiple Tenancy Multiple smart hosts Exchange 2013


I have a Exchange 2013 Multi Tenancy farm with a Big Mailbox Server hosting all the Mailbox Databases, each client has their own Mailbox Database on the Mailbox Server.  I have a Send Connector which transports all the e-mail out via a McAfee Smart Host.  The client domains are configured within the McAfee portal and a trusted ip is setup on the portal to allow my hub transport to mail too it.  Ok so far so good, this works fine.

If another client (mailbox Database) doesn't want to use McAfee for it's anti-Spam and wants to send via a different Smart Host for example Mimecast, the only way I can see is to add another Smart Host on the same Send Connector.  I understand that if you send e-mails through a Send Connector which has multiple Smart Hosts it chooses a different Smart Host each time to load balance them.  What I don't understand is what is happening behind the scenes if one of my clients from the McAfee account sends an e-mail out of my organisation and it chooses the Mimecast Smart Host or visa versa.  Is the e-mail just getting bounced back or is it failing a handshake and then choosing the other Smart Host? is this going to cause me problems?

Should I be using a third party tool which allows me to specify which domain inside my organisation can send out via different Smart Hosts?

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Simon Butler (Sembee)ConsultantCommented:
In most cases you wouldn't add another smart host to the Send Connector. You should create another Send Connector for the additional smart host.
However if the email gets rejected by the smart host, it will bounce - Exchange will not try the other one.

Exchange isn't really designed to route email based on the sender, it routes based on the recipient.
You will need to use a third party transport agent to do routing by sender.
Various options for those:


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ChallowSupportAuthor Commented:
Thanks Simon

That makes sense and I like the look of the Messageconecpt product, I'll give it a try.

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