Unable to set mailbox size more than default size in Plesk: The specified limit is invalid

Symptoms

Unable to change mailbox size in Plesk via the tab Domains > example.com > Email Addresses > click on mailbox > mark another size. 

Mailbox size typed in field  Another size is larger than the value defined in the Default size. Default size value can be viewed via Plesk UI: 

• For service Plan: Plesk UI > Service plans > Service_plan_name > Mailbox size
• For Subscriptions: Plesk UI > Service plans > example.com > Customize > Mailbox size
• For Resellers: Plesk UI > Reseller > John Doe > Customize > Mailbox size

The following error is shown in Plesk UI:

PLESK_ERROR: The specified limit is invalid.

Cause

Mailbox size is limited by Subscription / Service Plan / Reseller's Service Plan settings.

Resolution

Note: If you do not have Plesk administrator's access, contact Plesk server administrator and ask him to apply this guide.

1. Log into Plesk UI as administrator.

2. Switch Plesk interface to the Service Provider View.

3. Change the mailbox size limit for Subscription or for Service Plan or for Reseller. This depends on where limit is configured in specific case. There are 3 options:

Change limit for subscription

Go to Plesk UI > Subscriptions > example.com > Account section > click Customize > Mailbox size and increase limit to desired size.

Change limit for Service Plan

Go to Plesk UI > Service Plans > choose required Service Plan > change Mailbox size.

Change limit for Reseller

Go to Plesk UI > Resellers > the name of the Reseller that owns the subscription, domain or client > Account section > click Customize > Mailbox size and choose preferable size.