[Zope] Binding MailHost to an IP

Hi all, I have a box with multiple IP addresses that I use to support some internal development work. When using MailHost to send mail through an external mail server, I would like to have the mail "come from" one of the IP addresses in particular. It appears that the MailHost object is binding to the primary interface (eth0) instead of eth0:1, eth0:2, etc. Is there a way that I can specify a source address for the email? Thanks, Kevin