Read Permission for Mailbox

Problem Statement:

Can I grant Read Only Permission to a User's Mailbox (Cloud based service)?

Solution:

• Currently granting Read Permission to the entire Mailbox is not possible due to a Microsoft limitation.
• The Access Rights 'ReadPermission' refers to the ability to read the Permission on the Mailbox and it doesn't grant any permission to the mailbox (including Read Only).
• You can grant Read and manage delegation which is equivalent to Full Permission and it allows a delegate to open the mailbox and behave as the mailbox owner.

Read Permission is only usable for on-premise. It's not intended for end user's access.

To check other Mailbox Permission kindly refer to the KB article - How to Grant Access To Mailbox

You can however grant Read Permission at Folder Level using PowerShell or using Custom Action in CoreView.

Mailbox Folder Permission:

PowerShell cmdlet for Mailbox Folder level permission:

To add folder level permissions for users in mailboxes you can use PowerShell cmdlet - 

 "Add-MailboxFolderPermission".

This cmdlet is available in on-premises Exchange and in the cloud-based service. Some parameters and settings may be exclusive to one environment or the other.

Syntax:

Add-MailboxFolderPermission   
[-Identity] <MailboxFolderIdParameter>   
-AccessRights <MailboxFolderAccessRight[]>  
-User <MailboxFolderUserIdParameter>   
[-Confirm]   
[-DomainController <Fqdn>]   
[-SendNotificationToUser <Boolean>]   
[-SharingPermissionFlags <MailboxFolderPermissionFlags>]   
[-WhatIf]   
[<CommonParameters>]

Some Examples:

Add-MailboxFolderPermission -Identity ayla@contoso.com:\Marketing -User ed@contoso.com -AccessRights Owner

# This example grants the Owner role to Ed on the Marketing folder in Ayla's mailbox.

Add-MailboxFolderPermission -Identity ayla@contoso.com:\Calendar -User julia@contoso.com -AccessRights Editor -SharingPermissionFlags Delegate

# In Exchange Online, this example adds Julia as a calendar delegate to Ayla's mailbox, but without access to private items.

Add-MailboxFolderPermission -Identity ayla@contoso.com:\Calendar -User laura@contoso.com -AccessRights Editor -SharingPermissionFlags Delegate,CanViewPrivateItems

# In Exchange Online, this example adds Laura as a calendar delegate to Ayla's mailbox 
with access to private items.

For more information on Mailbox Folder Permission kindly refer MSDN article:  Add-MailboxFolderPermission