This is only in SmarterMail 14.X, and when marked as "internal only" will only allow mail to be sent to the aliases from an e-mail address on the same domain.
Anything sent to them from "outside" -- eg: from another domain, is ignored.
Bruce Barnes
ChicagoNetTech Inc
brucecnt@comcast.net
Phonr: (773) 491-9019
Phone: (224) 444-0169
E-Mail and DNS Security Specialist
Network Security Specialist
Customer Service Portal: https://portal.chicagonettech.com
Website: https://www.ChicagoNetTech.com
Security Blog: http://networkbastion.blogspot.com/
Web and E-Mail Hosting, E-Mail Security and Consulting