I've tested it with my local mail server, Postfix, and it sends pipelined messages through that just fine.

I started a little dirty hacking on it to get it to use NST as a base. Right now, I'm trying to focus on getting it to have two constructors. One takes Net::SMTP constructor arguments and returns on object subclassed from that. The other (which I'm calling new_tls() for now) takes Net::SMTP::TLS arguments and returns an object subclassed from that instead. I might switch focus to a separate module with just the TLS version if I run into too many roadblocks trying to keep it all as one. I'll keep you informed of any progress I make either way.