Nice to hear we are making some progress.
What you want to do at this point is right-click on an account and then select "Edit account..." from the context menu, then select the "Send Mail" tab in the left pane of the next window (see below) where you will then find the "Send option" settings. This setting should be set to "SMTP" if incoming mail (in the "General" tab) is either "IMAP" or "POP3", otherwise it should be set to "Webmail" in this window.
If what you get does not have the same 4 tabs in the left pane as illustrated above, more
specifically does not have the "Send Mail" tab then from the main menu go to "Tools" > "Plugins..." and make sure that "Send Mail" is enabled (checked) as pointed out in the screen-shot below.
If the plugin is checked and you do not have this "Send Mail" tab as pointed out in the first screenshot, then please post a screenshot of what you are getting (make sure and redact the email address, as I did, at top of screen-shot).
Also, assuming you do have the "SendMail plugin listed and it is checked (enabled) then make sure that its "Version" matches your version of POP Peeper (ie. v4.3.0.0) Note: If "SendMail" is either not listed or is old, then you need to re-install POP Peeper and make sure that "SendMail" is enabled (selected) in the "Choose Components" page during installation (the checkbox should be ticked). Note: If re-installing, do
not uninstall (simply install over PP).
One last thing, what do you have in the option pointed out below ("Tools" > "Options" > "General" tab)?
If you have a value that represents an Email Client that you do not have installed then that can pose a problem. If the problem persists and you have a value here, you could try leaving this option blank (doing so will result in your system default Email Client being used).
Good judgment comes from experience and a lot of that comes from bad judgment. - Will Rogers