Forum Discussion

sumo83's avatar
sumo83
Iron Contributor
Aug 06, 2025

Pop up window "Send blocked" for external users inconsistency with M365 E5

Hi experts,

 

I would like to get an advice on the experience we have after switching to M365 E5

We are using Sensitivity labels and one of them is INTERNAL. This internal label is then used in DLP to block it from sending outside the organization.

Before when with M365 E3, we had two different user experience when trying to send INTERNAL labelled data to external user:

  1. classic outlook - email was sent and after few moments, a notification email was received that the email was blocked for external recipients
  2. new outlook - a pop up window showed up when trying to send email asking to remove external user, etc - so the email was not even  sent if a user didn't fix either label or recipients - and this was a great feature.

Now, with E5, it is a bit inconsistent. Some users get a pop-up window (see attached picture), some receive a standard notification email once the email is sent.... etc. Using new outlook mostly so focusing on this one.

 

Is there anything I miss here? I really liked the feature that user are not even able to send email if they hit our INTERNAL DLP policy. 

 

Would appreciate any help,.. as could not figure this out for quite some time now :/

1 Reply

  • Prathista Ilango's avatar
    Prathista Ilango
    Icon for Microsoft rankMicrosoft
    Aug 12, 2025

    Hello sumo83,

    Few things to check,

    1. Is oversharing pop ups configured properly? Refer to: Get started with oversharing pop ups | Microsoft Learn
    2. Have you checked the outlook version used by these users for working and non-working?

    I would suggest to troubleshoot this by starting off with a clean test, 

    1. 2 users - one working and one non-working
    2. Confirm both has the same outlook versions
    3. Both has the same DLP policy and of top priority
    4. Make sure over sharing pop ups is configured properly as mentioned in the above article.
    5. Below option is set in DLP policy

    Hope this helps!

    Regards,

    PI

    Please mark as solution, if you find the answer helpful. This will assist others in the community who encounter a similar issue, enabling them to quickly find the solution and benefit from the guidance provided.

Resources