Mandatory Email TLS Mimecast and Office365


So we are working to configure Mandatory TLS security between 2 email domains. We have control of one, which we need to get this configured for.

They are currently using Office365 which routes through Mimecast for email filtering etc.

So my understanding of it is that we configure this on Mimecast only for incoming and outgoing mailflow, however, I am struggling to see how it works correctly, when it needs an SSL certificate from Office365 in order to work correctly?

Do we also need to configure inbound and outbound connectors for this TLS requirement on Office365?


Craig SummersAsked:
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Vasil Michev (MVP)Commented:
You dont need a SSL certificate "from Office 365", you simply need to provide the certificate details as explained here:
Craig SummersAuthor Commented:
Ok that part I've done. So do I only need to configure the TLS settings on Mimecast, or on both Mimecast and Office365 as Office365 is where the email would see the certificate?
Vasil Michev (MVP)Commented:
You need it on both sides if you want to enforce TLS for both sent and received messages.
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Craig SummersAuthor Commented:
The other company has already got it configured their end. I'm talking about just my end, we have Office365 which routes out to Mimecast before sending emails to receipients, and vice versa when people send to us it goes to Mimecast and then Office365. So with that, do I need to setup TLS on both of our Mimecast and Office365 portals? Or will just on Mimecast be sufficient?
Vasil Michev (MVP)Commented:
You need to set it up on every hop alone the route.
Craig SummersAuthor Commented:
OK, so both Mimecast and Office365 need inbound and outbound TLS routes configured. Thanks
Craig SummersAuthor Commented:
I only needed to configure it on Mimecast and not Office365
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