When attempting to send mail, Evolution reported that sending the message failed after DATA: "Operation now in progress". This error message was made up by Evolution and is meaningless. The mail server presented human-readable text which Evolution failed to display. I ran Evolution again with CAMEL_VERBOSE_DEBUG=1 but the mail went through on the second attempt, and the information about what went wrong was lost. Evolution should report the error message it receives from the SMTP server; it shouldn't make up its own. This problem was mentioned as an aside in bug #151121, but warrants a separate bug report of its own.
Have you seen this problem on recent versions of Evolution (Fedora 7 or later)? I notice one of the two upstream bugs linked to from here has been fixed.
The second bug (which is still open) is a duplicate of the first, which was closed by Jeff just because it was me who reported it, AFAICT. The problem still exists.
Fedora Core 6 is no longer supported, could you please reproduce this with the updated version of the currently supported distribution (Fedora 7, 8, or Rawhide)? If this issue turns out to still be reproducible, please let us know in this bug report. If after a month's time we have not heard back from you, we will have to close this bug as CANTFIX. Setting status to NEEDINFO, and awaiting information from the reporter. [This is mass-filed message to all open Fedora Core 6 bugs related to Evolution. If you see any other reason, why this bug shouldn't be closed, please, comment on it here.]
Closing this as upstream, we will track it in GN-bug #341579.