If you relay email from your internal network out through the Mailborder server, the Mailborder server needs to be included in your SPF record authorizing it to send email for you domain. Failure to do so will result in your email being rejected or quarantined by remote servers.
Building SPF records manually is not advised as it is too easy to make a mistake. There are sever free resources available to build these records for you.
Here is one: https://www.spfwizard.net/
How Mailborder Evaluates SPF Records
See this article for more information on the Mailborder SPF evaluation engine.