I came across a post on SO where the OP included their email address in the post (no link because I'm not sure of the privacy concerns). The address is in an excerpt from a debugging log file, and is in a code block so that only part of the text is visible (the address is around column 300 of the line) which is why I believe it was included inadvertently. It looks like a work email address; in this particular case, the OP's profile also has a link to a personal website, which lists a different email (I assume personal) address.
What should I do to warn this user (or any other user that makes the same mistake -- if it was a mistake)? A discrete email to the address I discovered? To the personal address on their profile? Flag for moderator attention? Ignore it?