By default, while subscribing to a mailing list on a website, running
Mailman (GNU) for mailing list management, the user has got options to
manage his/her subscription options.
There is an option of getting password reminder email for this list
once in a month.
And, by default, this option is set to Yes.
Along with sending the password reminder mail in *plain text* to the
users, it gets archived on the sites too.