While using the Sigsync service with a smart host third party services such as Proofpoint, Barracuda, Mimecast etc., you may find an email without the signature applied.


Follow the same steps for all smart host services. Here, we are using Mimecast as an example. The connector has been set to apply for all the messages at the connector level.



This setup shows the SMTP address of Mimecast smart host, but it ignores the Office 365 Transport rules. Therefore, we need to modify the connector and ensure that it will use a Transport Rule other than the Sigsync Transport rule. These changes ensure that the signatures are attached before the messages are scanned by the third party smart host services.

Follow the below steps to reconfigure connectors:

Step 1: Reconfigure the third party smart host service connector

  • Login to the Office 365 portal as a global administrator and open admin center.
  • Click the admin centers and choose Exchange.
  • Click on the Mail flow → Connectors.
  • Choose the connector to apply Only when I have a transport rule set up that redirects messages to this connector.


  • Retain all the other settings as they are by clicking the ‘Next’ button and save the connector.

Step 2: Add new mail flow rule

  • In the admin center, choose Rules, under the Mail flow, click on + to add a new rule.


  • Enter an appropriate rule name.


Step 3: Create new mail flow rule

  • Scroll down and click on the More options which enables the additional rule options.
  • Add a condition such as The sender is located inside the organisation. It makes sure all the emails sent from your Office 365 tenant will be routed through the connector.
  • Add one more condition such as The Recipient is located Outside the organisation. It makes sure internal email sent from your Office 365 tenant will be routed through the connector by avoiding mail loops.
  • Add an action such as Redirect messages to the following connector and then, choose the third party security connector.
  • Save the new rule and it should have a priority of 1. In the list, Sigsync rules should have a priority of 0. This ensures that Sigsync processes email and adds Signature and then Security service processes the email to make it secure.


Step 4: Modify the Sigsync mail flow rule.

  • Open the Sigsync Rule and scroll down, then check Stop processing more rule option. Click Save to save the rule.


  • Office 365 setup is complete now. You can send email and test the flow using message trace and also analyse message header

Want Free personalized service?

Sigsync email signature service offers company-wide and centralized email signature for Office 365 and Exchange.
We can assist you in getting your signature ready effortlessly.