php mail() slow

[thawebmaster]

Our server is really fast. I've never had problems with that, except one thing: if in php mail() is called, it takes 20 seconds to show the page.
I think the problem is in that outgoing mail is also scanned on spam. If an email is send using php's mail, php waits till the message has been send.
Is it possible to improve email sending in php?

Does anyone has any idea?
Normal smtp connections are very fast due to -Rt0

Thanks in advance!