Mail Transfer Services are only available in MAMP Pro.
If you have MAMP Pro, it can use the Postfix MTA (Mail Transfer Agent) that is built into your Mac OS X. It can also be configured to use an SMTP server.
With the standard MAMP Packages, you can only use an SMTP server. This means that with MAMP standard, you would only be able to test Universal Email if you have an SMTP server installed on the testing server.