Not had a chance to have a proper look at the Exchange package but it appears to be entirely web-based.
Not sure how that solves your problem. They might be better going for a web hosting package and uploading any excessively large files to the site for other people to download.
That way the get email addresses like
anamehere@theirorganisation.co.uk plus they can expand and have a web presence etc if they want it in the future.
The other advantage is that they can use their existing software (in this case Outlook Express) to download their emails. They aren't having to learn the new (web based) software that is used in the package you are quoting. Add all of that to the fact that web hosting would
probably work out cheaper.....
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I think the key thing to do here is to go right back to basics.
What do they need?
Why do they need it?
How often do they need it?
How much are they prepared to pay to get it?