Exim Sender Verify

We had a non-client (not on our server) that was getting 550 email rejections when he attempted to email us due to having Sender Verify enabled.

In the past I figured Sender Verify was necessary for fighting spam, amongst other things, but have realized that we may be having more rejections than we know because we never hear about them.

Is there a general best practice in terms of enabling Sender Verify or leaving it off? I've never heard about complaints about rejects from legitimate emails senders, so it doesn't seem to be an issue, but then again, you really never know...