Sometimes the words you use may be frequently used in spam emails.
It may be an affiliate link from a blacklisted site. Here are a few places to check before linking:
- Web of Trust:http://www.mywot.com/
- Google’s API:https://developers.google.com/safe-browsing/lookup_guide
Shortened links can be tricky, too, because they hide the URL and can be used to do harm. That’s why Email providers and the like often put a stamp on such emails.