Outlook Express Window Size

We have a customer who used 98 SE and Outlook Express 6.00. He connects to the internet with a modem and downloads his email.
Problem: A week ago, he was changing the screen size and font size to his desktop. In his attempt to correct his display settings, he messed with all kinds of things in the control panel. He does not remember all that he changed. Well we were able to get the display settings back to normal, but now there is a new problem.
Each time he opens an email message, the window size is about half of the monitor screen. He wants it set to full screen size, so he will maximize it to full screen.
Problem #2. Now, if he closes out that message and opens it up again, it will always be half screen size. He is wanting each message, when it opens, to be full screen size. No matter what we try, each message will only open to half screen size and he has to then maximize the window. He wants to have the message to always open to full screen.
Is there some setting, or registry setting where this can be adjusted? Thanks for your help.