If you send a large amount of emails every day or need to make sure that the emails you've sent don't go straight into the spam folders of their recipiens than this gig is the right one for you!
What does this gig offer?
Setting up a SPF, DKIM and DMRAC record on your DNS servers
Configuring dkim for postfix
Why is this important? Large email providers often have very strict rules for spam protection. In order to get your emails delivered to the inbox folder of your clients and not the spam folder you need these records so the email provider (of your client) can verify the legitimacy of your email.