Outgoing message disappears without being sent. What can I do?

Question

I purchase (my first) Macbook a month ago, after using PC for nearly 20 years. I love Mac!!!
Could not get Mail (2.1) to work in first instance, so started using MS Entourage. Would like to use Mail however.
Receiving mail works fine. When trying to send, the mail disappears totally. It won't appear in sent items, nor is it sent out. When trying to save the outgoing mail as a concept, it won't save (while the 'save in concept' button stays grey.
The connection to the server for both incoming and outgoing mail works fine.
Thanks for helping me out.
Vrolijke Hendrik
Macbook   Mac OS X (10.4.6)  

Answer 1

In the Finder, go to ~/Library/Mail/. With that folder open, do Edit > Select All (⌘A), then Edit > Copy (⌘C), and paste it in your reply to this post, to let me see the names of the files and folders present at the root level of the Mail folder.
Before actually posting that information, you may edit it so that the file/folder names do not reveal any details you wish to keep private, e.g. you may replace any real username with “username” to hide your real email address if you wish; similarly, you may disguise any domain names you don’t want to be revealed. Try to be consistent in how you disguise those details, though, as we may need to refer to them in subsequent posts.
Now, go to ~/Library/Mail/Mailboxes/. With that folder open, repeat the process to let me see the names of the files and folders it contains. Again, you may disguise any mailbox names you wish to keep private. Be careful to not alter any suffixes, though.
Finally, locate the account folders within ~/Library/Mail/ -- their name begins with the account type (POP, IMAP, Mac), followed by the account username and the incoming mail server. For each account folder, repeat the process to let me see the names of the files and folders it contains.