Send mails in the background

Hi,

Could you please let know how to enable sending mails in background instead of waiting for the mail to be sent. We want to reduce the visitor wait time while placing an order which takes more than 15 secs if smtp is used. if wp_mail is used it finishes in 5 secs. So we want to process the mail sending part as a background process. Can the post smtp submit the mails for processing as a background process?

Regards,
Murali