OE Duplicate Remover   
http://ajsystems.com

If you use Outlook Express for your personal or business mail you will, no doubt, have encountered duplicate email messages. The "Outlook Express Duplicate Message Remover" will automatically find and remove duplicate messages. The OEDMR will (a) find duplicate messages in any folder or group of folders; (b) match messages based on mulltiple conditions; (c) search by date or date range; (d) display, delete, or move the duplicates.

MailList Manager   
http://www.AdvertiserTools.com

MailList Manager is a tool for organize your emails lists. MailList Manager have many great features, such as merge lists, sort, remove duplicates, special filters and formats. MailList Manager have made managing lists of quick and easy. MailList Manager know how to Merging Lists, how to Split lists with size volume and Split Lists with domain filter. Remove Duplicates and Filter for Emails from one list specified into another list. MailList Manager can filter Emails with specified parameters from result lists. MailList Manager have Alphabetical Sort, Domain Sort, User Name or company sort features. Save Result with different formats - One Email per line format or separate mails by TAB or by Commas. Show Statistics for end list MailList Manager.

MailBoy 2004 MASS MAILER   
http://massmailersoft.com

MailBoy 2004 MASS MAILER - Easy to use yet powerful mass mailer. Built-in SMTP, built-in DNS, fast import and export of email addresses, ability to remove fast the duplicate addresses, 300 sending threads, ability to change the identity of the mailer, organize senders accounts and mail lists and much more. Also if you need an additional program's feature , you have the opportunity to ask the development team to add it in the next version.

EMailing List Pro   
http://petor.lab6.com

EMailing List Pro is a program for creating and managing lists of contacts (large or small), and then sending identical EMails out to all the people on the contact list. Includes many useful features, such as sort, search, select, etc. EMailing List Pro can save contact lists to files, and export and import Text and CSV files. It has many options for filtering contacts, e.g. prevent duplicates being added, and prevent contacts with invalid email addresses being added. Has support for Mail Merge, HTML format emails, File attachments, and Advanced scheduling.

Add-ins for Microsoft Office Outlook   
http://soft.ria-media.com.ru

RIA-Media Add-ins for Microsoft Office Outlook: Redirect, Duplicates, Attachments.