If you are using a provider like DigitalOcean or Rackspace and you are making use of their DNS management features. Then you might one day want to craft a SPF (Sender Policy Framework) TXT record.

The SPF allows email servers to check if the sending server is kosher and reject the incoming email or mark it as suspect based on the policy set in the SPF1 record.

The create the record you can use http://www.spfwizard.net/ which makes it easy.

Here is an example this TXT record is for jamesmcdonald.id.au

"v=spf1 a ip4:128.199.195.194 include:_spf.google.com ~all"

It basically means

allow any host with an A record in the domain (jamesmcdonald.id.au) to be able to send email.

Also set the host with ip 128.199.195.194 to be allowed

and also include the SPF TXT records for google (because that's my email servers and I don't want to manage the SPF records for their servers myself),

finally ~all mark any record that doesn't comply with the SPF as mentioned but still let it go which is  known as a SoftFail.