We send a weekly newsletter to our clients - about 5,0000 subscribers. We recently purchased a new mailing list software and we have been running into problems with clients using Exchange + Outlook (2007 and 2010).
At first we sent our newsletter as UTF-8. Clients using Exchange + Outlook received these emails as completely blank, while others received them correctly.
We then switched to encode them as Windows-1255 (Hebrew), and not they are getting them as gibberish. Again, other clients such as GMail receive them just fine.
We are defining each mime-part as charset = "Windows-1255". Is there something we are missing here? Some special custom header?