Open your Exchange Management Console.
Select the Organization Configuration → Hub Transport . Then click the "Send Connectors" tab.
From the list of connectors, right-click and select: New Send connector.
Enter the name of the connector. In this example, it will be named: Mailjet Connector
On the Address Space screen, click "Add".
Now enter an asterisk (*) in the Address Space field to relay SMTP traffic through Mailjet. Then click OK.
For a specific field domain, just enter its name, such as "hotmail.com" and validate. Then Repeat for each domain you want to add.
In normal operation, Exchange will send the mails for all domains using the default Send connector. For specified areas, it will use the Mailjet relay.
In our example, the Send connector will forward all mail via the SMTP relay "Mailjet".
Click ‘Next’ to continue.
Select Route mail through the following smart hosts
Click on ’Add ...’.
Now select Fully qualified domain name (FQDN) radio button.
Enter in-v3.mailjet.com. Click OK.
Click Next.
Select Basic Authentication.
Now enter the credentials of your account Mailjet, found on your SMTP Settings page.
The user name is the API Key field; the password to the Secret Key.
Then click Next .
You must now validate your configuration. Click Create.
The details of your connector is shown. Click Finish.
Congratulations, you just created your new connector!
Please note: the default port on your new connector is port 25. If you wish to use port 587, open your Exchange Management Shell.
Enter the command:
Get-SendConnector -Identity "Connect Mailjet" | fl 
The port is the standard port of the SMTP TCP25.
Enter the following command to change the port:
Set-SendConnector -Identity "Connect Mailjet" -port 587 
Then run the following command to confirm that the change was successful:
Get-SendConnector -Identity "Connect Mailjet" | fl 
Excellent! You just have to start the service Exchange Transport: 