Front-end SMTP program for Exchange

We currently use TFS Secure Messaging as a front-end SMTP server for Exchange. Therefore, all inbound email is scanned for viruses, filtered by content along with some other additional items such as stripping the header out of the email and attaching it as an attachment. We are having some minor problems with this program and was curious if anyone else used this program and if not, if you use a SMTP front-end for Exchange, what program do you use.

We also use TFS on the back-end of Exchange to attach a signature file for each user. This way each signature is the same and we can control the content in the signature.

Thanks.