Users who don't use their e-mail can lose their e-mail address or can encounter issues with being able to receive new e-mails. Below is few of the more common reasons why a user may lose his or her e-mail.

E-mail expires or disables with inactivity
Many free online e-mail services will either disable or delete an e-mail account that is not in use for so many days. For example, users who do not log into their e-mail account at least once every thirty-days can have their accounts deactivated.
Tip: Users who use Gmail, another popular free online e-mail service, will not lose their e-mail unless the account is dormant for 9 months.


However, almost all users who pay for their e-mail or their e-mail is provided by their Internet Service Provider will not have their e-mail disabled or discontinued. However, you may encounter quota issues as explained below.
If your e-mail address has become disabled or discontinued, you will permanently lose all the e-mail you have received as well as any e-mail addresses or contacts kept by the service.

E-mail exceeds allocated quota or allocated message count

Although exceeding the allocated quota (your account's available storage space) will not disable your e-mail account, it will prevent you from receiving any new e-mail messages. To help save disk space, many e-mail providers give each user only so much space to store their e-mail online. Which means if you do not maintain your e-mail or download your e-mail onto your computer often enough, you can run out of space and be unable to accept any new e-mail messages.