How To Know Stored Email Volume on PlusNet?

[#1]

Is there a way to know the volume of email stored for the account by mailbox?
I've received a note from PN stating that I need to reduce my stored email volume. Is there a way to find the volume stores either in total, or preferably for each mailbox? Whilst some clients (eg Outlook) will give you this data I'd like to avoid surveying all mailboxes individually especially as some are for other members of the household.
Given that PN must have some way to monitor it doesn't seem unreasonable to ask for the same visibility.

[#2]

The CSC can provide this information if you call or raise a ticket. However DIY solutions either require using an email client such as Thunderbird with the Extra Folder Columns add-on, or using webmail.
If you log into webmail, select Personal Settings and the Folders tab, the properties list for each folder shows a Size line with Click to get folder size alongside. Click and it tells you. It is necessary to do that for each folder and add the values up (take care with the units).
Each mailbox needs to be checked individually.

[#3]

Happily my request on the ticket for a list resulted in a schedule of volume against each mailbox being returned to me.
Would be nice if there were a page on the portal under 'manage email'