Could not access delegated/impersonated shared mailbox via EWS

[Yasitha Pandithawatta]

I am trying get mailbox folders using global admin account credentials via EWS. I am using the following ruby script with viewpoint gem to do it.

require 'viewpoint'

include Viewpoint::EWS

endpoint = 'https://outlook.office365.com/ews/exchange.asmx'
admin_email = 'admin@hostname.com'
password = 'password'

user_email = "user@hostname.com"

cli = Viewpoint::EWSClient.new endpoint, admin_email, password
cli.set_impersonation 'PrimarySmtpAddress', user_email  #impersonation
act_as_hash = { act_as: user_email }
results = cli.folders(act_as_hash)

puts results.count

I have created required permissions and impersonations for all the mailboxes. I am having a issue when accessing shared mailboxes. I can access user mailbox folders using the same script.

When I tried the above script to get shared mailbox folders I am getting following error.

/Users/yasitha/.rvm/gems/ruby-2.3.0/gems/viewpoint-1.1.0/lib/ews/connection.rb:121:in `check_response': SOAP Error: Message: The primary SMTP address must be specified when referencing a mailbox.  Code: a:ErrorNonPrimarySmtpAddress (Viewpoint::EWS::Errors::SoapResponseError)
    from /Users/yasitha/.rvm/gems/ruby-2.3.0/gems/viewpoint-1.1.0/lib/ews/connection.rb:103:in `post'
    from /Users/yasitha/.rvm/gems/ruby-2.3.0/gems/viewpoint-1.1.0/lib/ews/connection.rb:81:in `dispatch'
    from /Users/yasitha/.rvm/gems/ruby-2.3.0/gems/viewpoint-1.1.0/lib/ews/soap/exchange_web_service.rb:212:in `do_soap_request'
    from /Users/yasitha/.rvm/gems/ruby-2.3.0/gems/viewpoint-1.1.0/lib/ews/soap/exchange_data_services.rb:503:in `find_folder'
    from /Users/yasitha/.rvm/gems/ruby-2.3.0/gems/viewpoint-1.1.0/lib/ews/folder_accessors.rb:45:in `folders'
    from o365_test_connection.rb:14:in `<main>'

I tried to comment the impersonation line and use delegation to access the mailbox folders but I get the following error.

/Users/yasitha/.rvm/gems/ruby-2.3.0/gems/viewpoint-1.1.0/lib/ews/folder_accessors.rb:167:in `find_folders_parser': Could not retrieve folders. ErrorNonExistentMailbox: No mailbox with such guid. (Viewpoint::EWS::EwsFolderNotFound)
    from /Users/yasitha/.rvm/gems/ruby-2.3.0/gems/viewpoint-1.1.0/lib/ews/folder_accessors.rb:46:in `folders'
    from o365_test_connection.rb:14:in `<main>'

Can anyone help me on this?