Note, that Rapportive does rate limit their service: http://www.quora.com/Rapportive/Does-Rapportive-Rate-Limit http://www.quora.com/Rapportive/Does-Rapportive-

Note, that Rapportive does rate limit their service: http://www.quora.com/Rapportive/Does-Rapportive-Rate-Limit http://www.quora.com/Rapportive/Does-Rapportive-Rate-Limit So, while this does work, you might run into limits depending on your usage. Interestingly, my company (SalesLoft) does the same thing, but against actual mail servers. While SMTP is a seemingly simple protocol, the actual implementation of it can vary greatly and wrangling it is quite a challenge. But if you can take it on, it works about 60% of the time to get you a working email address.