Slow email opening on iMac with Monterey 12.7.6

My wife's old iMac, using Monterey 12.7.6, takes a very long time to open her mail. The program opens quickly but it takes at least 10 minutes before the individual emails open and can be read. Aside from the obvious and most practical solution of getting a new Mac, is there any other solution to overcoming the problem?

Thanks in advance for any help that can be offered.

[Re-Titled by Moderator]

Original Title: Mail very slow opening