I hope you're joking!
Responding to spam with spam is as illegal as sending the original spam in the first place - many of the email addresses in spam headers are not "real" but are some poor bystander's address coopted by a spammer. If you send them a marketing message back, you ARE spamming and can risk having your hosting shut down, being sued, etc.
It could do a massive amount of damage to a commercial company being spamvertised in that way.
Think of it like this: just because a burglar has broken into your house, that never greenlights you to break into theirs!