[Zope] sending mail slow?

Hi, I've noticed that sending mail from within Zope the <sendmail> tab or mailhost.send() is very slow (like it adds a few seconds to the time it takes to get a page back from a post). Why is that? how can I make it faster? I'd thought about having the actual mail sending done in a different thread/process but I don't know how I'd do that or whether it'd be worth doing. I wonder where the slowness is coming from :S cheers, Chris