RE: Canīt decrypt mails with Lotus Traveler Companion 2.05
The text/html content type is probably a hint, but we'd need to know what the html was. The most likely HTML is the Domino login form (the shaded yellow box) for wrong credentials, but the connection should have failed in the Settings then too.
The best thing would be to open a PMR with HTTP thread logging enabled (tell http debug thread on) so that we can see the text/html body. Of course, you may want to use a test encrypted mail for that and not something that you don't want us to see.