While our environment in exchange 2007, we do run one non-exchange iis smtp server, using tls encryption that forwards everything to exchange. It's beginning to get hit hard with spam attempts and there are no really good tools for managing. Can I use zimbra as a replacement for this server. Just needs to be able to support TLS, which I read it does, using domain credentials. Seems like it does everything I need, so I'm just looking for a reason I shouldn't consider this option.