Are my emails in MS Outlook the same in my default outlook express

[seniorlarito to the rescue]

I use and look at Outlook Express (default) for my emails but have found out
that MS Outlook file also have them listed, is this necessary and should I
delete the MS Outlook emails to manage my space and does this affect my
storage on Outlook Express?
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[neo [mvp outlook]]

When it comes to storage of email, they each have their own way of storing
items. As for each containing some of the same content, at one point,
someone had to start Outlook and let it import account, address book, and/or
messages.

My advice, pick which program you want to use, configure Internet Explorer's

Options > Programs tab to use the program you want as your default e-mail

program + address book.