By default the system will use our own servers to send email.
If you're using a customised sender address then you may want to use your own servers to reduce the chances of the email being seen as spam.
Click your employer name in the main menu and go to Settings -> Mail Settings
Tick the box labeled 'Custom SMTP Settings' and you'll be able to enter details of your own SMTP server.
Remember to save your changes before clicking the 'Test Settings' button to ensure everything is working as expected.