I have Jenkins version 1.480.3 installed on my machine and Email-Extension Plugin 2.28.
I have configured my jobs on Jenkins and everything works fine except the fin
Looks like a bug in the plugin. Here's a workaround:
In the global settings for the plugin make sure to provide a full e-mail address for System Admin E-mail Address, (e.g. foo@bar.com, not just foo), even though you've specified the Default user E-mail suffix. The address itself can be bogus, though.