✅ Step 1: Log in to Plesk
Go to your Plesk panel address (for example: https://yourdomain.com:8443).

Enter your administrator or user login and password.

✅ Step 2: Go to the “Mail” Section
In the main menu on the left, click Mail.

You will see a list of all mailboxes for the domain.

✅ Step 3: Edit Mailbox Settings
Click the name of the mailbox you want to limit (for example: info@yourdomain.com).

You will be taken to the mailbox settings page.

✅ Step 4: Set the Limit
Find the Mailbox section.

Make sure the Mailbox option is enabled (checkbox is active).

Below, locate the Mailbox quota (MB) field.

Enter the desired value in megabytes (for example: 500 means 500 MB).

If you set it to 0, the limit will be removed (not recommended).

✅ Step 5: Save Changes
Click OK or Apply to save your settings.

Done — the new limit will take effect immediately.

ℹ️ Additional Information

• If you have multiple domains, make sure you are editing the mailbox for the correct domain.

• To set a default limit for all new mailboxes, go to Service Plans → Mail → Default size.