Microsoft Exchange allows for implementation of S/MIME encryption and signing that more or less "just works." There are some naggles (I've run into people befor

Microsoft Exchange allows for implementation of S/MIME encryption and signing that more or less "just works." There are some naggles (I've run into people before whose Outlook was S/MIME signing emails to external uses, and my Outlook would be upset about showing them since the external user's cert was signed by some internal CA I didn't trust - if I didn't know what was going on that have lead to a frustrating helpdesk call). But, overall, it's nearly transparent when everything is as it should be. Unfortunately, outside of the world of these internal corporate email products the situation looks a lot worse. Reliably secure delivery of email to external users is a hard problem and most of the current solutions being used are really, really terrible.