Instant Customer not on any global spam blacklists: We monitor those lists regularly and work with spam watchdogs to maintain that status.
However, that does not prevent spam filters from tagging your emails as spam based on the content. If your emails are getting spamfiltered, the problem is almost certainly the content of the email. The solution is to change the content of your message so as to be less suspicious. And remember, suspicious doesn't just mean ads for pills and discount watches: Malware has been distributed as love notes, meeting reminders, and all sorts of other seemingly innocuous traffic. So if your message is getting flagged, it may resemble any of the billions of spam messages sent in the past.
If you're not receiving your notification emails (which is quite common), whitelist Instant Customer in your local spamfilter.