Storage space management

Storage space management

I have Zoho CRM Plus which doesn't include Zoho Mail but seems to need it to manage email within the CRM... - I am actually thoroughly confused about this... anyway....

Since the last update to CRM I noticed mail conversations no longer display in all areas of the CRM along side contacts and leads. I thought I should open Zoho Mail and see if the issue is there.

Sure enough mail had stopped due to going over the 5GB space. It still doesn't explain everything but I should clear this up - easy right? Nope.

I deleted all the email in Zoho Mail and cleared the trash and spam and guess what? I only got 2GB back. What you say? Yes, only 2GB came back after clearing all my mail. 

So what gives? Is this shared between accounts on CRM Plus? If so, where do I manage that storage?