Why am I receiving duplicate emails from the same sender

[Cindy]

My Outlook email is linked to my boss' Outlook email account. I log in as
him and then have total access to his email. Recently, when I receive a
"read receipt" from him, I get five emails, all the same date, time, size.
Also, If he is replying to my email, I get five replies from him, all the
same date, time, & size.

Please let me know the source of this issue.

Thank you,
Cindy