Outlook allows you to use another SMTP relay than your main server. Please review your company’s internal security policy about using an external SMTP relay to send all your email. as it may not be authorized.
Before making any changes, please record the current SMTP settings in the event you need to revert back.
Once you are in Outlook, go the Tools menu, then Account Settings. Select the email account you want to modify, then click Edit.
In the Outgoing server field, enter: in-v3.mailjet.com
Click ’Additional settings’ (or ’More Settings...’) button, then click the ’Outgoing Server’ tab.
Check 'My outgoing server requires authentication'. Enter your User name (API Key) and Password (Secret Key). You can find your API & Secret Key information on the SMTP Settings page.
Click the ’Advanced Options’ tab. and Outgoing Server , specify port 465 and choose the type of encryption SSL.
Close by confirming all settings windows and then send a test message to verify that everything works.
If needed, just check out our documentation:
• Outlook 2010
• Outlook 2011
One more thing: the campaigns you will send through Outlook won’t display as regular campaigns on your account. To see the status of your recipients, just check your Stats page.
Credit : https://www.mailjet.com/support/how-do-i-change-my-smtp-settings-in-outlook,98.htm