Office 365 MS Outlook stops displaying base64 html images over time

Darren Braynard 1 Reputation point
2021-03-15T14:52:13.087+00:00

MS Outlook displays base64 img tags for a while, but then at some point, Outlook fails to render the img tags and shows only a black square. Below is a gist of a sample html file that I'm using as the body of an html email which demonstrates this. When Outlook fails to render img tags, it then cannot properly render any email with base64 img tags. Outlook seems to have an internal rendering class or service that crashes and Outlook must be restarted to recover its rendering ability. It seems that resizing the outlook window can trigger the failure, but that is not consistent.

https://gist.github.com/dbraynard/273a16f2593e85b385f36ae8f1e08f07

Outlook Management
Outlook Management
Outlook: A family of Microsoft email and calendar products.Management: The act or process of organizing, handling, directing or controlling something.
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  1. JeffYang-MSFT 6,241 Reputation points
    2021-03-16T06:16:08.543+00:00

    Hi @Darren Braynard ,

    Are you using Outlook 365 desktop client? If so, what's the version of your Outlook 365? (File > Office Account > About Outlook). Please make sure you have upgraded your Outlook to the latest version.

    MS Outlook displays base64 img tags for a while, but then at some point, Outlook fails to render the img tags and shows only a black square.

    Not quite sure if I have understood your issue properly, in order to test about your issue, I tried the steps below in my Outlook 365 desktop client:

    1. Create a .txt file, copy the HTML codes you provided in the link to this file.
    2. Rename this file as .html file and open in Web Browser.
    3. Using Outlook 365 (Version 2101 Build 13628.20528), copy the content displayed in Web Browser to new Outlook email message, using HTML format and send it to myself.
      78122-1.png
    4. All the content seems just display normally all the time.
      78096-2.png

    In order to conduct further research about your issue, as I know, there are some related-settings in Outlook which might cause similar issues. Please ensure that "Don't download pictures automatically in HTML e-mail messages or RSS items" is un-checked(Open the Outlook window, click on File, Options, Trust Center, Trust Center Settings, and then click on the Automatic Download option) and see if the issue has any difference.

    By the way, there could be some add-ins in your Outlook client that cause this kind of display issue, so it is suggested to start your Outlook in safe mode (Press Win + R, type “outlook /safe”, press Enter.) and see if the issue continues.

    Any update, please feel free to post back.

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