If mail and news is open, and my email account is selected, I can compose an email, send it, and it will go in the sent folder. If I have a newsgroup selected, press ctrl-m, change the field to To: instead of News: and put someones email address in there. When I send it, it doesn't go into the sent folder. If I'm in the browser, with mail and news closed, press ctrl-m and send off an email, when I go back to mail and news and check the sent folder, the message I sent is not there. No matter when or how I send it, it should be placed in the proper sent folder. Right now the data seems to be going to byte heaven.
In the case of sent news-messages, you will likely find them in the "Local Folders" sent folder. That is the default, unless you have configured particular news-servers differently. As for mail-links triggered from browser, it seems that if mailnews is not open but a news-server was the last selected, sent mail lands in "local folders" sent-folder as well, since the initial identity is assumed to be that of a news-server. Resolving as dup of bug 105838, where reporter wishes that mail-links in browser should use the default mail-account identity. *** This bug has been marked as a duplicate of 105838 ***
verified as dup