Email harvesting is the process of collecting lists of email addresses using various methods.
Usually used for bulk emails or spam. Hackers use "harvesting bots" that crawl numerous sites, chat rooms, web forms, etc. for a few seconds to retrieve a list of email addresses
There are different techniques for collecting email addresses:
• Posting to UseNet with email addresses.
• Yellow Pages data collection.
• By accessing the same computer used by valid users
• Access email and address books on another user's computer.
• Spam through social engineering.
• Buying lists from other spammers.
• Hacking websites.
• Hacking mailing lists,
• From Web pages
• From a Web browser,
• From internet chats,
• From domain contact points,
• From finger daemons,
• Through the Ident daemon.
The methods listed allow spammers to collect email addresses and then use them to send unsolicited mass messages to the recipient's inbox.