Splunk in itself has no SMTP server and so cannot out of the box receive emails. However thanks to scripted inputs you can do all kinds of weird (and wonderful!) things to get data into Splunk. Simply put, set up some kind of solution for
- Receiving emails (use your SMTP server of choice...postfix, sendmail...)
- Extracting the contents of these emails (some kind of script)
Once you have that in place, Splunk can run the script as a scripted input and consume the script's output, thus getting the data from the emails into Splunk.