http://www.phplist.com/
http://www.contractoruk.com/lists/?p=subscribe&id=1
Requirements -
- Allow users to add themselves to lists via a web form. Yes
- Validate users email addresses when requesting addition Yes
- Allow users to maintain themselves - i.e. remove themselves/change email address. Yes
- Control who can send to each list and send suitable error to those who aren't allowed. Not sure what you mean
- Integrate with my current web host's email system to send/receive Yes
- free or cheap Yes
- Must be web based as I don't have access to the server itself. Yes
- can be either .NET or PHP scripting PHP
- can be either MySQL or SQL Server 2005 database MySQL
- My hosting provider supports POP, IMAP & SMTP Erm
- Allow users to add themselves to lists via a web form. Yes
- Validate users email addresses when requesting addition Yes
- Allow users to maintain themselves - i.e. remove themselves/change email address. Yes
- Control who can send to each list and send suitable error to those who aren't allowed. Not sure what you mean
- Integrate with my current web host's email system to send/receive Yes
- free or cheap Yes
- Must be web based as I don't have access to the server itself. Yes
- can be either .NET or PHP scripting PHP
- can be either MySQL or SQL Server 2005 database MySQL
- My hosting provider supports POP, IMAP & SMTP Erm
Works very well! If you use it and need any help give me a shout.

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