Unless you are going to block a huge amount of spam by doing it then it is probably not a good idea.
Yes, from what I can tell, iHug started doing this recently. Wait, no, they are checking that my mail server would accept messages for the envelope sender address. Because mail from a bunch of users' PHP code has an envelope sender of apache(a)hostname (but a valid "From:" header in each email), I have to accept mail for apache(a)hostname (or at least pretend I do). it's not really a /huge/ problem, but it's annoying to have to do so. Infact, I haven't bothered yet.
Another thumbs down for Ihug. I am dealing with rejections from Ihug because the envelope-sender address that my PHP driven systems use, is web-server-owner(a)mx.host. IF it were simply @domain, it'd work fine, but the MX record for my domain does not in itself have an MX record, and is not actually configured for mail... So far, its only Ihug that has a problem, and only recently - but what bothers me is that it ignores the 'From:' and rejects based on an inability to validate the envelope-sender. I havn't taken any active steps to 'fix' it yet, as i'm yet to see why its 'broken'. Apparently Orcon employ something similar, but I havn't had any bounces from them yet... (maybe its just a matter of time...) Mark.