list accounts with duplicate email addresses

I searched for a module that did this first, but didnt find one. Is there one? What do you think about putting this in contrib on d.o? (It will be my first contrib module, and should have pretty low, but not nil usage.)

I have written a module (for a project I'm working on) to list accounts that have duplicate email addresses.

Right now, it has two blocks, one is a custom sql query that lists all the accounts with duplicate email addresses grouped by email. The other is a block generated from views, that is to be used on user account pages that just lists all accounts that use that email address.

I started writing a README.txt which I include to give a better idea of what the module does:

-- SUMMARY --

The Duplicate Mail module has a block to display system wide duplicate email addresses
in user accounts, and a view with a block display for use on individual user
account pages that displays only the accounts that have the same email address as
that account.

This is to be part of a suite of modules to be used in a non-profit member
management system (which includes batch import/creation of users based on csv
files).

For a full description of the module, visit the project page:
http://drupal.org/project/duplicatemail

To submit bug reports and feature suggestions, or to track changes:
http://drupal.org/project/issues/duplicatemail

-- REQUIREMENTS --

Views module.

-- INSTALLATION --

• Install as usual, see http://drupal.org/node/70151 for further information.

-- CONFIGURATION --

• This module lists user account information, including email addresses. Restrict
  access to this information by configuring the blocks to only display for a
  siteadmin type of role. (Picking a role other than anonymous or authenticated
  will make it so anonymous or simple authenticated users cannot see the blocks.)
  Configure block role visibility in Administer >> Site Building >> Blocks
  and configure the Duplicate Mail blocks under Role specific visibility settings.

  Also, change the region from Disabled to some other region. Right sidebar works
  well for the system wide block. And content or content top works well for the
  individual block generated by views.

-- TROUBLESHOOTING --

• If the blocks do not display, check the following:

  • Make sure you save the block settings page after moving the blocks to a new region.

-- FAQ --

Q: It's impossible to get accounts with duplicate emails; why have this module?

A: There are a few modules that bypass that safeguard and allow duplicate emails.
And, during an import of users using the migrate module, accounts can be created
using emails already in use by other accounts.

This module is useful for listing only the accounts with duplicate emails so that
the users can be contacted to correct the situation, the accounts can be merged,
or just for information purposes to find out how many duplicates there are.

-- CONTACT --

Current maintainers:
* Cathy Theys (YesCT) - http://drupal.org/user/258568