Not sending emails to people who have given you their email address because you don't want to bother them, piss them off, or have them unsubscribe is ridiculous.

It's most likely not how many emails you send; it is what you are sending them.

Every advertising medium works best with frequency; your email is the same. Find people who want to be on your list, and make sure they hear from you at least once a week, even if you're just saying hi!