Mail not loading message content(s)

So in mail, I have it to where I have to double click to open a message so that way I can cut down on spam. I know there is a way you can have it to where it is a split screen and the bottom half of the mail shows you the content. I don't do that to avoid verifying a valid email address for messages that might slip thru filtering.

Every now and then mail won't load the message(s) when I double click them and open them in a new window. I have asked this question before for my Mac Mini but can't find the thread. I saw a thread that said something about IP filtering. Yeah my system doesn't do that via Network in System Preferences.

Attached are screenshots of mail, system info, and versions. Yeah I know I'm running an older system but when the M3 iMac comes out, if it does I will be upgrading.

Thanks for any help.

-Jimmy