For your mail to arrive at its destination, it must be addressed EXACTLY right!  This means all the dots and other symbols are in place; no spaces are in the address; upper and lower case is used correctly; zeros are zeros and o's are o's.  One tiny mistake (like a comma instead of a period) can cause your mail not to reach its destination. 

Typically, e-mail addresses look like this: 
  

There is no reliable directory of e-mail addresses. Those that do exist gather up addresses from public postings. Unless you've posted a message to USENET or entered your address at some popular Web site, your address won't likely be listed on a directory. The largest directory of e-mail addresses is Four 11. You may be lucky enough to find an old friend there. 

Address Books 
  
Nearly all mail programs have an address book feature that lets you save frequently used addresses and associate them with nicknames.  Once you've put an address in your book, you need only to direct a letter to the nickname; the appropriate address will be inserted automatically. 

The address book function also lets you group addresses so that you can address several people at once by just choosing the group nickname. 

Look through the options on your mail program's menu bar to find the Address Book functions.  Experiment with them.