Minimal setup for sending mail from webapp only

I have not set up any email services on my linode since until now there has not been any need.

However, I recently installed GitLab and it seems to insist on sending out password resets links to new users (of GitLab, not the linode) by email.

What would be the minimal setup for this? There is no need for users on the linode to receive email - all the email address targets for users will be elsewhere. I just need to allow GitLab to send email.

Of course when I say minimal, I am still very concerned about security.

The Linode is running Debian 7.

Thanks for any advice. For some reason I have always been intimidated by email services. :)