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How do I configure Office365 to send messages through the outgoing filter?

To use the outgoing filter in conjunction with Office365, you must first create an outgoing user in EuropeanMX. We recommend that you create the user as "Authenticating Domain" and activate the setting "Re-authentication permitted". More informations can be found in our FAQ article "How do I set up an outgoing user?". After you have defined an outgoing user, you must create a transport rule in Office365. To do this, proceed as follows:


Log into Office365 Administration Center.


Click on "Mailflow" and go to the connectors.


Create a new connector with Office365 as "From" and Partner Organization as "To".


Select "Only when I have a transport rule set up that redirects messages to this connector".


Select "Route email through these smart hosts" and add "".


Activate the checkbox "Always use Transport Layer Security (TLS) to secure the connection (recommended)" and select the option "Issued by a trusted certificate authority (CA)".


Validate the connector and save.


In the Exchange dashboard, go to "Mailflow" and select "Rules".


Use the plus sign to add a new rule.


Assign a name to this rule.


Click on "More Options".


Enter the value "The sender's domain is..." for "Apply this rule if...".


As the sender domain, enter the domain that you previously added as an outgoing user in EuropeanMX as "Authenticating Domain" (similarly, you can specify a rule only for certain sender addresses).


For "Do the following..." please enter "Redirect the message to", "The following connector".


Specify the Smarthost Connector you created previously.


Save this rule.

Once set up, any traffic that matches your outgoing sender domain should be routed through the transport rule and processed by the filter servers.

Please note that our servers only accept a maximum of 10 connections from your server. This ensures an optimal delivery speed. To prevent that you get the message "421 Too many concurrent SMTP connections from this IP address; please try again later" and the messages are stored in the queue, the connection limit of 10 connections has to be kept.

The hostname of our relays is "". Please make sure that you use port 587. If this is not the case, the messages will be rejected and not sent with the error message "550 Relay not permitted!

IMPORTANT: If you use our outgoing filter for your messages, you must change the SPF entry in the DNS settings of your domain. This should look like the following:

v=spf1 -all

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