The best policy is to never link through email solicitations.
Try to stick with people who post here or whom you know otherwise.
Exchanging links with strangers or scraper sites etc can hurt you. If you do link exchanges through the mail you need to follow up daily on them or you could end up linking to a site google banned – and get hurt yourself.
A lot of these mails come from black hat sites. Another bunch from link farms. Bad stuff. And very annoying, too.