Version: (using KDE 4.3.1) OS: Linux Today I wanted to send a mail to a large number of people. kmail showed me that it couldn't send the mail, but didn't give me any reason for it. Luckily I had the possibility to look into the server logs and found 431 Too many recipients. there. But it's really bad behaviour to not let the user know any reason for an smtp-failure. It should pass the server error message to the user so the user get's at least an idea what might be the problem (as most users probably have no way of looking into the server logs).
What SMTP server was used and what was the number of recipients (to be able to reproduce it) ? Can you check the exact message kmail showed ? Sidenote: I think that the error code returned from this server is not correct. RFC 2821 says that error codes starting with 4 are temporary errors: "A rule of thumb to determine whether a reply fits into the 4yz or the 5yz category (see below) is that replies are 4yz if they can be successful if repeated without any change in command form or in properties of the sender or receiver (that is, the command is repeated identically and the receiver does not put up a new implementation.)" But I assume that the number of recipients is a server implementation limit and therefore a hard limit.
The server is courier. The strange thing is: I can't reproduce it any more. If I do it now, I get a long list of error messages from the server... Same server, same kde version, no real idea what changed. About the error code: I'll check that.