When processing my email, instead of deleting the stuff I do not need to keep or act on, I transfer most of it to a holding folder called "Hold 60 days" which automatically deletes contents older than 2 months. In practice, this is very much like trashing the messages, but if for some reason I need to retrieve something in the near future, I still have a second chance. It works like a recycle bin.
My logic is that there is a lot of stuff that I probably won't need again but there is a small chance that the issue will rear up again and I will want the email for reference. If that doesn't happen within the next few days or weeks, then it can be safely considered a dead issue and the messages deleted. I really do not want the overhead of archiving and then later culling out such things because the volume of these items is huge and that would require handling each one again in the future. This is an efficient way to keep it retrievable for a while with no overhead. This also makes it easier for me to dump things that should be dumped without that nagging feeling that I JUST MIGHT need it someday.
It is probably also possible in some email programs to simply set the "Deleted Items" folder to delete items only after 2 months so you can look there to retrieve stuff that you have an unexpected need for.