RecoverableItemsQuota is one you can set in the Hosting plan and Mailbox plan of the customer.

In general it should be 6143 or higher by default (i normally recommend setting 6500), 0 or unlimited are not valid values in this case, due to exchange calendar size restrictions it has to be configured correctly before exchange can change the mailbox space.

SolidCP does not support editing exchange/ active directory accounts outside of SolidCP (it does not pull all the information live off the AD / Exchange server).