To set the quota on email address please follow the following steps:-
1) Login to Plesk control Panel.
2) Click the "Domains" shortcut in the navigation panel
3) Click the required domain name in the list.
4) Go to Mail Accounts.
5) Click on "e-mail address >> Mailbox".
6) Select the box in front of Enter size under "Mailbox quota" option and enter the amount of
space you want to give to that email address.
7) Once you have entered the amount of space click on "OK". The quota has been set
on the email address.
Note:- By default the quota is selected as Unlimited which means that this email
address may use any amount of space provided to that domain.
