This article gives advice that is not only bad, but dangerous. You should never, under any circumstances store a password in a format that can be reversed. Doing so for the password to someone's primary email address borders on criminal - a comprised email can be used to break almost any other account someone may have.

If there's no other way to build the app, don't build it. It's the only ethical thing to do.

that's a bit extreme. in order to log into gmail accounts via imap, you have to have the email and password for an app like that: http://jeffreifman.com/filtered-open-source-imap-mail-filter...

It's not unethical to build such an app.