MESA - Meta E-mail Search Agent
This does a search of many e-mail directories. If you don't find an address here, it still could exist, as there is no complete source on the Net.
MIT Usenet Address Search
Search an e-mail directory compiled from Usenet postings within a certain date range.
College E-mail Addresses
This service helps to locate e-mail addresses for undergraduate and graduate students. There are many links with helpful hints.
PostMinderSM
From the developer: "The online equivalent of certified postal mail, PostMinderSM notifies you when emails are opened, read and forwarded. Digital certificate technology verifies emails with timestamps and datestamps. And advanced features, such as virus protection and self-destructing email, ensure your total control." This is a subscription service - it is not free. The service apparently works even when the recipient has disabled return receipts.
Reverse E-mail Search
Find the name behind an e-mail address; there's also a search to find ICQ e-mail addresses.
FreshAddress.com
If you change e-mail addresses, you can report it here. Then, if someone inquires about your new e-mail address, the service notifies you and you can say whether or not you want the party to have your new e-mail address.
Free Email Address Directory
This site has listings for over 1000 free e-mail services. User comments about various services are included. There are also resources to help you find e-mail addresses.
Tips: If you know where a person works, most companies have web sites. Many of them have online directories of the e-mail addresses of staff. If someone works in a government position, their government e-mail address is public information. If you know the school a person attends, most schools have online directories. For graduates, there are often alumni directories.