It sounds as if you may be trying to operate in Preview mode instead of the normal List mode. I did not see you state but I assume you are running the latest v4.63 released in January of 2012. To go to normal List mode click the List button on toolbar. If you are seeing three pane display of mail then you are using Preview mode.

Reply address, user/account plus domain may be set. Return path is not normally used and is normally constructed using the sending SMTP server information. Many of the older return path mechanisms were male obsolete in current RFC5322. Even  if you specify a reply address there is no guarantee the receiving mail client will use it and may depend, as with Pegasus Mail, user setting whether to use reply or the From: address. Some may even have elected to use both for replies.

Are you also using Mercury/32 as your mail server or something else? A normal SENDMAIL type server? Take a look at raw view of incoming mail message and see what entries have been added at various hops along the way. Most of what you have asked about are server functions and entries placed by hops along the way. Many may not  be included depending on the POP3 server you are receiving your mail thru.

Hi All,

When I click on the first email header details in the top panel, it flickers but does not get selected (turn blue). I have to click it again to select it.

If there are more than one emails listed and I click on any one BUT the first one it is selected as it should be with the single click.

 What's up with that?

 Thanks

If I understand the question correctly, the first click is making the new mail window active then the second click selects the message.