Also, note that the carat (^) anchor isn't necessary. The header fields you're testing for are in the left most position. Thus no reason to left anchor your expression.
Of course there is.- Anchored expressions are executed faster (the parser has to check the pattern only against the beginning of the line).
- If I write an e-mail with the following subject, the OP would get a false-positive:
Subject: Wrote an e-mail to: ad...@domain.tld
