Helped with unblocking attachments in outlook emails

Don Campbell 21 Reputation points
2020-07-14T14:28:48.33+00:00

I have an exchange hybrid deployment with an exchange 2010 server and all mailboxes migrated to online. All clients are using the latest Office 365 32-bit desktop client. This setup has existed for several years but more and more recently, users report that attachments from external senders are being blocked that did not even a few months ago. Sometimes the email can be moved to the junk folder and then right-clicked and choose unblock sender and the attachments appear, but this is not an ideal solution. For a specific example, .jpg gets blocked. I have looked in the attachment filtering and .jpg is in the allow list. It is quite possible that I am not looking in the right place and I would like some direction or information on documentation to help me try to diagnose this. Any suggestions or pointers would be greatly appreciated.

-Don

Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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Microsoft Exchange Hybrid Management
Microsoft Exchange Hybrid Management
Microsoft Exchange: Microsoft messaging and collaboration software.Hybrid Management: Organizing, handling, directing or controlling hybrid deployments.
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Accepted answer
  1. Manu Philip 16,991 Reputation points MVP
    2020-07-14T19:52:52.037+00:00

    Hello Don,

    Outlook and OWA will auto download images for addresses in the Safe Senders list. You can control this by Safe Senders list to all clients via Group Policy and/or Registry settings. Check a reference here: how-to-deploy-junk-email-settings-such-as-the-safe-senders-list-by-usi

    Please mark as "Accept the answer" if the above steps helps you. Your suggestion will help others also !

    Regards,
    Manu

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  1. Yuki Sun-MSFT 40,871 Reputation points
    2020-07-15T08:07:31.367+00:00

    .jpg is not listed in the Blocked file types in Outlook list, so normally it won't be blocked in Outlook. Regarding the Attachment Filtering, when an attachment matches an entry on the attachment filter list, the Attachment Filtering agent can be configured to Reject/Strip/SilentDelete, while blocking attachments is not included. See Set-AttachmentFilterListConfig.

    Given this, if you would like to troubleshoot further on this issue, I'd like to suggest checking if it can be reproduced in OWA. Besides, considering that some attachments might be removed or blocked by antivirus software used by the organization, you can check if there are any attachment filters setup in your antivirus software or try temporarily disabling it and check the result.

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