webpromo,
1. If you enter the minimum requirements for a client, email, password, first and last name, they will be able to login to the client side of DotNetInvoice and update the rest of their information. Does that take care of what you need?
2. Would it work if you added a note about updating contact information when you send out invoice emails?
3. We've had a few requests for this and have it in our tracking system.
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Jeremy
DotNetInvoice Support