A service for sending, receiving, and/or storing email, usually on a remote web server, in such a way that it is accessible through a web browser.(noun)
The email thus stored.(noun)
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Use "webmail" in a sentence
"Drafting a long important e-mail in webmail and then hitting “send” only to find your session has timed out and the e-mail is * gone*."
"Though this is miles and miles better than the privacy that plain webmail delivers, there are a couple of ways in which this is less than perfect -- the system doesn't protect the To: and From: and Subject: information in your email; an adversary might be able to harm you just by knowing the fact that you've gotten encrypted mail from a specific person."
"Update - webmail is busted, I'll deal with that in the morning."