Here are answers to your questions.
The email account type is POP3.
We don’t use webmail. As previously stated, we use Outlook. The appearance of messages when opened from the browser is
identical to their appearance when opened directly from Outlook.
It happens with all messages. The font size within an open message is constant between messages. It is too small within
the message body, and smaller still in the message header.
Before I requested your assistance, I did re-set View. With everything at default, I then changed font to a larger size
by selecting File, selecting Options, selecting the Mail tab, selecting Stationary & Fonts, selecting the Personal Stationary tab, and changing all fonts settings for the three options, new messages, replying and forwarding, and composing. This affected the
body of outgoing mail. However it had no effect on the body of incoming mail.
Also, working outside Outlook, I right-clicked the desktop, selected Personalize, selected Window Color, and changed the
font settings for all items having a font option. This increased the text size on the Ribbon, Menu bar and Quick Access toolbar. However it did not affect the header of open mail messages.
I have changed settings such that messages are converted to Plain Text, expecting that a consistently formatted body will
enable enlargement of the body font in all messages by re-setting a default font (the same presumably also being true for the message header).
The reading pane is also not being used, and it will not be used, as my wife has a visual disability and needs her entire
screen to read messages.
Brian