Why is the Mail App on my iMac slow to download emails?

This is second or third time posting for this same issue. The mail app on my iMac (macOS Monterey 12.7.5) is slow to download emails, and sometimes just goes into the color wheel of death. I have re-started the app and have completed the mailbox rebuild many times; this does not seem to help. It is just a frustratingly slow processing; comparing to my iPhone, iPad, and MacBook Pro - none of these devices have the same issue, only the iMac. Aside from taking a hammer to the iMac, anyone have a solution to this ongoing problem? Thank you.

[Re-Titled by Moderator]