Hi SunilKms,
You can try the following cmdlet
This returns permissions on the mailbox by its SMTP address.
Get-MailboxPermission -Identity | Format-List
For Example:
Get-MailboxPermission -Identity john@contoso.com | Format-List
The above example returns permissions on the mailbox by its SMTP address john@contoso.com.
You can also refer other syntax of Get-MailboxPermission by using the below cmdlet
Get-help Get-MailboxPermission –examples
Thanks,
Archana