Best Reverse Email Lookup Tools Online
Spokeo: Spokeo is definitely one of the most comprehensive people search engines on the Internet. It aggregates information from public sources all over the web to find as much information on people as is publicly available. There are various subscription tiers, depending on how much information you're looking to find, but for basic email searches, it can be as low as 2.95/month (for a 1 year subscription).
People smart: People Smart is also fairly comprehensive, though maybe not quite as much so as Spokeo. However, if email addresses are all you're interested in, it will serve just as well, and the cheapest membership option is priced identically, at 2.95/month for 1 year.
Email Finder: This is a unique people search website, because unlike most of the general or telephone number specific options available, this site only searches email addresses. Generally speaking, services that specialize in only doing one thing tend to do them pretty well, so if email information is all you're concerned with, this might be a good place to look, and because of its limited nature, it's also a little bit cheaper than the other options, at 1.95/month for its 1 year memberships.
Keep in mind that privacy is taken pretty seriously on the Internet, just like anywhere else, so these lookup tools are only providing information available from public sources. Private information is no more available here than it is anywhere else. Also, if you don't want people looking you up, all of these services will allow you to opt out of their results, but don't forget that even if your information doesn't appear on their site, it still exists in its original form, somewhere on the Web. Always be mindful when providing your information to any public source online, because if it's public, it's visible to anyone.