The act of purging your inbox of e-mails kept for a very long time, probably due to reluctance to either:
A) Remove an e-mail you may need information from later, but probably won't.
B) Take the time to remove the unwanted e-mails.

Derived from the words enema and email, this is a compulsory evacuation of unwanted e-mails from your inbox which can extend to e-mails sent months or years ago. This will rarely happen if you check your spam often.