When it comes to filtering email the potential market is vast as almost everybody who receives email receives SPAM. Realistically any company wishing to generate a sustainable user-base must pick its target market carefully.
The mail-scanning.com service was initially designed to meet the needs of a technical user who was struggling to keep up with the influx of mail on their own personal domain(s). In our experience many technically competent administrators reach their limit and decide that some problems are better outsourced to a third party. However they typically still retain a healthy amount of skepticism and like to be reassured will not suffer from their providers mistakes.
Many existing SPAM filtering companies, or individuals, are very controlling and offer few opportunities for their users to make changes to the way their mail is handled. (For example a service might allow you to import the list of valid email addresses belongin to a domain, but offer little in the ability to control the handling of their mail beyond that.)
In some senses allowing an external party to make the decisions for you is for the best:
You're not simultaneously paying somebody to do a job and helping them do it.
You probably don't care how the junk is filtered, you just wish it to be removed.
Even if you did wish to be involved chances are you don't have the time, patience, or experience required to micro-manage the services' settings.
When it comes to filtering email mistakes can and will be made, and allowing the end user input into the process allows these mistakes to be mitigated. Cutting down mistakes is a good thing, both for the filterer who has to deal with fewer support issues, and for the end user who sees an increased accuracy from the service.
If you allow the user to make changes they can ensure they are not subject to similar repeated failures.
Even if the user-changes aren't significant they will feel in control.
Over time our service changed focus as we found more users who wished to re-sell our mail filtering product, with custom branding.
Re-selling existing solutions can be particularly attractive to hosting companies, small ISPs, and other similar businesses because it allows them to offer a service without the overhead of developing, maintaining and supporting it directly.
Due to our core idea that a user could host an arbitrary number of domains, each of which could be modified and tweaked independently, it became particularly attractive to resellers, as they could offer different levels of service. For example they might choose to offer a "high-end", "mid-range", and "basic" spam-filtering product:
The basic product would be a domain that the reseller added to their account with most of our checking processes disabled.
The mid-range product would be a domain the reseller added with more options enabled.
The high-end product might have all tests enabled, and allow access to the online quarantine of rejected mail.
As it became apparent that resellers were going to be a significant source of revenue we made changes to our service to support the way that they operated. We also offered branding possibilities for clients such that they could disguise the fact that they were merely reselling an external service.
(i.e. Rather than users visiting http://mail-scanning.com/, they could view their online quarantine at http://quarantine.reseller.com/ and that would take them to their archive of rejected mail. Only the reseller would use our panel to make changes to the domain.)
No assessment of a target market would be complete without an examination of the people already operating there.
Due to the decisions we'd taken we generally regarded ourselves as having zero competitors - in the sense that none of the existing mail filtering services offered a combination of things that we did:
The ability for end-users to change settings on a domain-wide basis via a comprehensive online control panel.
A searchable online quarantine area containing every single piece of rejected mail for the past month.
An level of transparency above and beyond that usually available in the field.
A small admin team, each of whom understood the service from top to bottom.
The ability to access complete SMTP-level logs for every email ever processed.
That said there are obviously other companies offering anti-SPAM services to the public at large, and it is regrettable that few of them were interested in maintaining dialog with ourselves. Too many companies seemed more interested in keeping their methods and techniques secret. This was particularly regrettable in the case of the smaller companies who primarily focussed upon wrapping existing software behind a closed door and providing little real innovation and few distinguishing features of their own.
At least part of the reason why we were open in discussing the operation of our service was because sharing techniques with others in the field provides a net gain for all of us. SPAM is a global problem and realistically no single group, company, or association is going to make much of a dent in the problem alone. Only by sharing information, observations, tools and techniques, can filtering companies hope to stay ahead of the curve and improve the detection of SPAM for themselves and their customers.