I don't believe there is a built-in or easily obtainable Technology Add-on (TA) for SBG - I did a bit of searching before answering this question here and didn't see one.
However, it sounds like you are asking on how you would get your data into and searchable in Splunk, and only secondarily about specific TAs or Apps.
So if you don't have your data coming in yet, that should be your first task. George Starcher's blog may be a good place to start for ingesting syslog data into rsyslog or into my preference, syslog-ng. Set the email device up to send syslog in to whatever server you create for doing syslog (it can be quite modestly sized - it just needs enough disk space), and install the UF on that syslog server.
You'll then configure a monitor input on the UF on the syslog server to read the files syslog-ng/rsyslog is creating. Set your sourcetype and index in that monitor stanza - for help, see this section of the inputs.conf. Set your outputs.conf to go to your Splunk Indexer.
Additional help can be found by searching the rest of Splunk's documentation (Awesome stuff!), search Answers, or even post a new question about some specific task you are having a hard time accomplishing!
