For those bioch users who haven't yet moved to Herald, the inbox soft and hard quotas on opal are 5 and 20 Mb respectively.
Other saved mail folders do not take space out of the inbox quota. They are instead counted against your home directory quota.
For the majority of bioch users, who have
now moved to Herald, details are available at the link below. Note that the Herald quotas relate to all your mail folders, not just your Inbox