It is very easy to migrate an entire SM installation from one server to another. Is that what you mean? Or do you mean that you would want a tool that migrated just users from SM to another mail server (mail, contacts, calendars, notes etc..)?
Moving from SM to SM is very easy either way. You can move your entire installation or per domain/user.
As for moving from SM another mail server software, I agree, a tool would be nice, but I think that would be the responsibility of the mail server software you are moving to and not SmarterTools.
There were some 3rd party utilities that helped with moving TO SmarterMail. I remember there was one for Imail to SM, Merick to SM and a few others. They may still be available somewhere, but the Imail one no longer works :)
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