Every domain is allocated a certain amount of mail storage space on the WebPlus.net server which is then shared equally between all of the email addresses associated with that domain.
See the table below for more information:
||Mailbox space allowance
||Number of email addresses
For example, if you have a platinum hosting package with 10 email addresses, each email address will have 40mb of storage space available.
There are a number of effective methods which could actively reduce the amount of space that your mailbox uses. For more information, read this related Knowledge Base article - FAQ - How can I manage my mailbox storage more effectively?