You'll just have to guess. To evaluate the reliability of a particular directory, do a search to see if your address is listed. If you strike out with directories, don't give up. Try another approach. Check business cards.
Many people list their e-mail address on their cards and stationery, so look there.
Mine old messages. If you've received a message from someone in the past, it contains the person's address. Mail, automatically record the sender's address in your address book. This should open a box that displays information about the sender. Search for online references.