Correct.  The credentials stick until Pegasus Mail is restarted.  If you don't want to have to enter your credentials for each session then enter them in the configuration of that POP3 host.

Tools > Internet options > Receiving (POP3) tab

I can receive mail fine. I've been user of Pegasus for over 13 years, but now I can't send mail without the following error message. I do not remember changing any settings? I use Windows 7 Professional. Here is the error I am getting:

Delivery has failed on the enclosed message for the following
reasons reported either by the mail delivery system on the mail
relay host or by the local TCP/IP transport module:

   554 5.7.1 <2000@vineyard.net>: Recipient address rejected: Access denied

Your original mail message follows:
--------------------------------------------------------

X-PM-Identity: <Default>
Date: Wed, 28 Oct 2015 16:44:24 -0400
MIME-Version: 1.0
Subject: ll
Priority: normal
X-mailer: Pegasus Mail for Windows (4.70)
Content-type: text/plain; charset=US-ASCII
Content-transfer-encoding: 7BIT
Content-description: Mail message body

Check with your ISP to see if authentication requirements have changed.

Got sending mail working, but the first email I send each day, I now get a dialog box asking for info to Establish a POP 3 connection? After I fill that in, Im all set that day?