My favourites are Red handed and All Killa, No Filla. Love that they're both presented by British women around my age who are funny and engaging, they do a lot of research!
I also listen to:
Wine and Crime - 3 drunk Americans who drink wine and chat true crime, this is the most laid back of them all with the littlest detail but they have funny stories and confessions so you can dip in and out
True Crime Garage - 2 American men, ones voice is just like Rossi from Criminal Minds, they've had John Douglas the famous profiler on their show and really get in to their cases
Seeing Red - another British pod, but more serious
They walk among us - one man presenter with a lot of detail
Crime Junkie - quite short recaps of famous cases
Morbid - mixture of murders and spooky stuff
Crime Weekly - this is quite new and it's presented by youtUber Stephanie Harlowe and a police man so tend to be very detail focused
Thank you for replying - I'm glad you're looking at other types of penpals too as like many have said there are plenty of lonely people out there, for me I was interested in whether it's inmates specifically you want to engage with and if so why but obviously that's not the case.
All the best with it and stay safe