SPF

Before Braintree can send emails from your domain, you need to add the following to your SPF record:

include:spf.braintreegateway.com

A full example of an SPF record might look like this:

v=spf1 a mx include:spf.braintreegateway.com -all

a allows servers listed under the A record for your domain to send email. Similarly mx allows servers listed under your MX record to send email for your domain. -all indicates a hard fail, which means if email is sent for your domain from a server that isn't listed, it will be denied. If you're setting up SPF for the first time, you should be careful to include all hosts that send email for your domain. You can also use ~all to indicate a soft fail.

For more information see the Wikipedia page on SPF.