[t0astbread]

I was thinking of the case where your server has to send out bounce mail but I guess if it's configured right, it should also just relay that.

[dugite-code]

Yup bounce emails are routed just like any other email so they go through the relay. This is actually one of the gotcha's when using fetchmail, you can accidentally send out a lot of unintentional bounce emails from an invalid server if you are not careful.