I like how the service has one download which includes email tracking, email encryption, document signatures and file sharing for large files all from one applcation. I use their Outlook app. Review collected by and hosted on G2.com.

I would like to have an app for my mobile phone that does all of this too but it isn't too big a deal since I don't use my mobile email client for business emails. Review collected by and hosted on G2.com.