I first got in touch with the Perforce support team about this Issue and got this response.
"I have had a chat with the developer of p4jenkins and he has said this is not something he has control over as it is the "Email Extension Plugin" that is making called to P4Jenkins for each changelist.
My recommendation to you would raise it with the developers of Email Extension Plugin and ask them for a option to only show last changelist and not all changelist since last successful changelist.
From my understand of the code they are making a call for each changelist from last successful build to the last build number. This is why your getting all these descriptions."
I followed their recommendation. We run a 1.625.1 Linux Jenkins server with a 2.40.5 "Email Extension Plugin".