When you look at my email inbox, you will find thousands of emails read already but still sitting there in my inbox occupying space. I can’t delete most of it because the emails contain important information which I know I will need anytime. Well, I am just one person. Imagine how it is with companies with several emails set up for their employees. I am sure that it is eating up a lot of server space.
If you want, there is an email archiving services that the company can avail of. Archive those emails. Anyway, it can still be accessed. What’s important is that it won’t be hogging the resources meant for the easy flow of operations.