This article is describing a brief guide on how to prevent internal users from auto-forwarding emails to external mailbox users and on how to disable automatic email forwarding in Office 365 and Exchange Server.
Allowing users to use mail auto-forwarding brings the risk of information leakage. Additionally, users can select the option to not keep a copy of the message in the mailbox which could also result in data loss.
Sep 22, 2011 Disable EWS Access for a particular Mailbox. EWS feature access is not segmented to allow access to particular EWS operations — it’s all or nothing. Turning off EWS will affect clients that use the OOF settings, availability, mail tips, and so on. It is important to take this into consideration when planning the client-server interaction part of your system architecture.
How to remove the automatic email forwarding options from Outlook on the web (OWA) in Exchange Server and Exchange Online
Automatic email forwarding options in Outlook Web App in Exchange Server and Exchange Online
In Exchange administrators control which actions can be performed by the users through Role Based Access Control. To remove the option shown in the picture above you need to modify the Default Role Assignment Policy. The Default Role Assignment Policy contains a Management Role called MyBaseOptions which is holding the parameters responsible for the forwarding and letting users perform the desired changes through the graphical interface of OWA by running Set-Mailbox on the background :
DeliverToMailboxAndForward
The DeliverToMailboxAndForward parameter specifies the message delivery behavior when a forwarding address is specified by the ForwardingAddress or ForwardingSmtpAddress parameters.
ForwardingAddress
The ForwardingAddress parameter specifies a forwarding address for messages that are sent to this mailbox. A valid value for this parameter is a recipient in your organization. You can use any value that uniquely identifies the recipient.
ForwardingSmtpAddress
The ForwardingSmtpAddress parameter specifies a forwarding SMTP address for messages that are sent to this mailbox. Typically, you use this parameter to specify external email addresses that aren't validated.
As you can’t modify the build-in role MyBaseOptions, you need to create a new role to replace it with.
Removing any existing auto-forwarding left from before the implementation of the new role
As the forwarding can be set to both internal and external recipients you might want to export a list of the mailboxes which had configured the settings before the Role Assignment Policy modifications. This will allow you to remove only the forwarding to external addresses with precision:
Get-Mailbox -ResultSize Unlimited -Filter {(RecipientTypeDetails -ne 'DiscoveryMailbox') -and ((ForwardingSmtpAddress -ne $null) -or (ForwardingAddress -ne $null))} | Select Identity | Export-Csv c:ForwardingSetBefore.csv -append
If you want to remove any kind of forwarding regardless the location:
Get-Mailbox -filter {(RecipientTypeDetails -ne 'DiscoveryMailbox') -and ((ForwardingSmtpAddress -ne $null) -or (ForwardingAddress -ne $null))} | Set-Mailbox -ForwardingSmtpAddress $null -ForwardingAddress $null
Disable forwarding set through Inbox Rules
As the Inbox Rule are frequently created by the users and can’t be blocked on server side (unless you disable the creation of Inbox rules which allow forwarding and redirection as described HERE), you need to disable this on a Remote Domain level.
The cmdlet below will disable the forwarding to all external domains. If you want to restrict this for particular domains only replace you can do so as well. Set-RemoteDomain Default -AutoForwardEnabled $false
Or you can clear the selection for the Default Remote Domain settings from Exchange Admin Center > Mail Flow > Remote Domains
As that setting will be applicable for all newly sent emails but will not eliminate the rules, you can use the cmdlet below will export a list of the mailboxes which have forwarding, redirection or message deletion rules configured, review them and remove them upon demand as well:
foreach ($a in (Get-Mailbox -ResultSize Unlimited |select PrimarySMTPAddress)) {Get-InboxRule -Mailbox $a.PrimarySMTPAddress | ?{($_.ForwardTo -ne $null) -or ($_.ForwardAsAttachmentTo -ne $null) -or ($_.DeleteMessage -eq $true) -or ($_.RedirectTo -ne $null)} |select Name,Identity,ForwardTo,ForwardAsAttachmentTo, RedirectTo, DeleteMessage | Export-Csv c:tempInboxRules.csv -append }
Remove-InboxRule -Mailbox [email protected] -Identity 'RuleName'
Note: In case you are facing an issue with corrupted or hidden Inbox rules, yet you still want to remove them, please consult the following article.
Another option which you might consider, as it will be notifying your users as well, is to configure a transport rule to handle the blocking of any auto-forward message types:
Note: Applying the following action 'Enable Client Rules Forwarding Block Advanced Action' from Secure Score in Office 365 Security and Compliance Center will create a new transport rule for your organization.
It will stop external messages leaving your Tenant, that are of the type AutoForward, mitigating the use of Client created external mail forwarding rules and malicious Remote Domain entries as a data exfiltration vector. If The Sender is located 'Inside the organization' If The Recipient is located 'Outside the organization' If The message type is 'Auto-Forward' Reject the message with the explanation 'External Mail Forwarding via Client Rules is not permitted'
The steps mentioned above aren't going to be reflected in the Secure Score. In order for you to obtain the Action Score Points you need to apply the rule from Secure Score.
Active3 months ago
I am using EWS API in my console application to process mailbox items and my connection script looks like
But i found that my email account was moved to Office 365 cloud. How should i change the authentication ?
i found EWS service url
but i dont know how to use it.
Thank you
Muflix
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2 Answers
You can use the code below to connect to the EWS on office 365:
You need define one callback function for the AutodiscoveryUrl function, like this:
ataravati
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MattMatt
I know this is a fairly old solution, but it was still very helpful to me. I have a few tools that worked with the 'normal' network version of Exchange, but so far my tests with Exchange Online failed (i got errors like 'The Autodiscover service couldn't be located', etc).
Essential here is to use WebCredentials instead of NetworkCredential and a e-mailaddress instead of a username.
GeeBeeGeeBee
protected by Community♦Jun 12 at 14:33
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