A Medium Webmail System is a combination of four elements (or more!): Mailing Service, User Managment, Log System and Message Store.

Mailing Service:
I am a experienced webdeveloper in Active Server Pages and Java Server Pages, for a Webmail System experience, I recommend that u use Active Server Pages because it's very simple than JSP and have rapid deployment, look at www.easymail.com, there are several components that will help u do a really cool WebMail based System.

User Managment for Domain:
For user managment on the Webmail System (Create accounts, etc), I recommend the aspuser component (www.aspuser.com), with it, users (or administrator) can alter their username, password and u can log some cool things, how user last logon, last logoff... a really cool component.

Log System:
A cool log system will terminate with your headaches, users that delete message and say they didn't do, things like that, for log system I recommend the use of FSO (File System Object - an Asp included object) working with tab delimited text files.

Message Store:
For message store, I recommend that u use a database system like Oracle 8i or Sql Server 2000 (7.0 no!). U can make tables that store deleted messages, sent messages, contacts and drafts from your users.

Well, is that, it's a medium complexity web mail based system, I hope that u can undestand, 'cause my english is horrible!:0)

Regards,

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Alv