[sylpheed:36889] Concatenate Separated Messages

I am running Sylpheed 3.5.0 on Linux and noticed under the tools menu,
just below the command "Delete duplicated messages" the command
"Concatenate separated messages".

I wanted to save the text of a thread of messages to a text file on my
disk and thought this would be a great way to do it. I highlighted the
emails and selected the command and got the message

	Error: The selected messages cannot be combined.

So, I went to the manual (at
file:///usr/local/share/sylpheed/manual/en/sylpheed.html) and looked for
the command, but it was not there. Then I noticed the manual was written
in 2002 for Sylpheed-0.8.10.

So what is this command? How does it work? Is there a newer manual?

Thank you,


Craig