An internet session log should help identify the sending problem.

One thing to check right off the bat...

In the Security tab of you SMTP host configuration is a setting called "Only use SSLv3...".  It should be unticked unless you are in the very rare circumstance of needing to use an old implementation of SSL.

Replaced former desktop computer after lightning strike. Have reinstalled Pegasus, but the preview pane shows up. I don't like this and didn't have it  before. How do I turn it off?

Which preview pane are you referring to, the one that displays previews of attachments or the one that displays previews of messages (3 panes in a window titled Folders - New mail)?

If the later, you are running in Preview mode and probably want List mode.  To switch, click the "List" button in the header of that window.

Like I said, I was sure it was simple. Done and fixed. Now to figure out why i can receive mail but not send it.