I agree with @codinghorror that this opens a “can of worms”, but it would help some of our users currently. The reason is because we’re allow “email-in” to post topics or replies. However, many of our users have multiple e-mail addresses, and I’ve seen that they don’t always consistently use the “correct” one in their profile to send things in. Because there’s no notification of failed posts, they just assume their reply/post worked correctly and never think to go back and check.
I’m not sure that this is a good approach, but as things stand at this moment, I feel a duty to +1 this suggestion on behalf of my users who have had difficulty using Discourse as a result.