(Plesk for Linux) Mailbox Quota Notifications
Mail users receive email notifications when more than 95% of their mailbox disk space is occupied.
In the Horde and Roundcube webmail clients, mail users can also see the information about the mailbox storage disk space, its usage, and limits.
Mailbox quota notifications for mail users are enabled by default. To turn them off, add the following lines to the panel.ini file:
[mail] enableMailboxQuotaWarning = off