First off, thank you, Scarab for posting your workaround script. We appreciate your participation in the Community.
Secondly, I just wanted to send a quick note that an option to force HTTPS will be included in SmarterMail 16.x, which is currently in BETA and will be available within the first quarter of this year. The setting will be found by System Administrators in the Miscellaneous Settings > Server Info section. The following settings will be available: Require SSL and Allow domains to override SSL Requirement.
Prior to enabling this setting in SmarterMail 16.x, you must ensure the product is set up as a site in IIS and have a valid SSL certificate in place on the server. SmarterMail 16.x is currently in BETA, so keep an eye out for the final release! ...Coming soon!