I do a fair amount of monitoring around if someone's mailing list has been stolen or not and in the past have manage mailing lists of over 1 million emails each.
When monitoring I've seen just about everyone have their mailing list stolen including much larger firms like banks or large retailers. The worse offenders have been mailing list service providers that either intentionally sell their customers emails or have security problems.
When you have a large mailing list, people find out about it. So people who spam or want access will use just about every means to get access to by either software security issues or by calling the hosting providing and trying to social engineer access to the servers.
It is a problem and it does happen regularly to a large amount of firms.
The way I prefer to solve these problems is to stop it at the source,
1. Make sure email provider and or software handling emails is secure - encrypted user data and safe backup storage.
2. Only give access to highly trusted people and or don't provide access to interfaces that allow downloading of list
The monitoring is done by spam traps and a manual check of email messages going to the spam traps. These emails appear like regular email address and only receive emails from one source. If a list is compromised then usually more then one spam trap will receive the comprised email. This triggers an audit of where the compromise has happened.
My response to your product is
1. First off there is no description of how your service works, there is no trail period, no indication of how you are going to track these people down, how you are going to do the detection.
2. It indicates that the email list size is 10,000 emails, which implies you require uploading of the emails. This is a major no no as you increase my risk of email theft
3. The product would only be helpful to me if I could monitor several mailing list sources rather then mailing lists
4. The price does not matter as you've no only proved no value you are more likely to increase my risk and cost based on the current presentation.
5. To check a few spam traps the cost is minimal and does not increase with the size of mailing list but does increase with the frequency of mailing. I'd have to actively monitor 20 or more mailing lists to justify a service.
6. If you take it from a perspective of someone who is not familiar with the security issues around emailing lists you need to provide some backing to show why this service is needed and how it is costing customers money if at all. Hell lots of customers receive spam hence spam filters.
Overall the though of a firm providing this type of service is of interest but your current offer would unlikely result in me trying a trail let alone a signup. I'm open to discussing this over a call if you need additional input.