You need to setup an SMTP relay, using the Nanorep service IP address list.
Please refer to Microsoft instructions:
Once you have the SMTP relay configured, the next step is to configure the SMTP settings in your Nanorep account.
This is done by clicking on Settings-->Ticketing-->Ticketing Basics.
You only need to specify the FROM address and the SMTP host. Other fields are not relevant. See example below: