tried with empty encoding too, no luck

btw, I don't think you need to add special support for utf-8 if you use .NET classes to send e-mail (the doc link you posted says .NET will use BASE64 or whatever encoding needed if you say the mail is in Unicode [UTF-16] or UTF-8 or UTF-32).

Just make sure you don't parse manually that encoding string, but use .NET's classes to get an Encoding instance out of an encoding name (let me know if you can't spot the way to do that, had done it at LvS project [http://www.codeplex.com/LvS] but don't remember at the moment if it was totally straightforward like using a constructor or there was some factory method elsewhere)

As for mail headers, they use their own encoding scheme that contains the encoding at the start of say the from, to etc. fields in something like ?encoding? (if I remember well) with the encoded data following - .NET should be taking care for it (checkout PHP's mb_encoding_mime_header for examples [e.g. see discussions at end of page])

Aha!

Was using "myself@somewhere.com;someother@somewhereelse.com" there and it was choking on it (should it? does it expect "," there to send to many people or doesn't it support sending to many people at all? - I think you should make a splitter that works with both "," and ";" and makes an array of mail addresses to feed to .NET if it doesn't support it directly)

Thanks for looking into the better logging too, would have helped if I could see that string since I'd go and search for where else it may have been defined in the GUI (had set it when I first set up the contact form and didn't remember about it being there to guess that was the issue)

support for non-latin e-mail bodies is too needed if it doesn't exist already

also from what I understand you can define the mail template at email.config or something? Why not define/edit visually a template (and maybe have dropdown to choose from some ready made ones and add yours there too [with option to be portal global maybe if user is admin]) at the contact form settings and/or at site e-mail settings?