Hope your very well. You can modify the maximum space available for attachments within the staff permission sets. You'll need to login to your Admin CP, click Staff (in the navigation bar running along the top), then click "Staff Permissions.
You should see one default permission set for all staff members. If you click the name of the permission set this will take you to the general options for that permission set. Towards the bottom of this screen you'll see an option called "ATtachment Space".
I've attached a screen grab here to show the option below. I hope this helps.
Kindest Regards,Ryan Healeyryan@instantasp.co.ukwww.instantasp.co.ukBlog | Community | Docs
For free (personal) users, we offer unlimited storage (not based on number of emails) but it is bound by the per day usage quota and for Business users, the storage limit is based on the pricing model and the per day quota based on the usage pattern.