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DarrenBraynard-0686 avatar image
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DarrenBraynard-0686 asked DarrenBraynard-0686 commented

Office 365 MS Outlook stops displaying base64 html images over time

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

office-outlook-itpro
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1 Answer

JeffYang-MSFT avatar image
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JeffYang-MSFT answered DarrenBraynard-0686 commented

Hi @DarrenBraynard-0686,

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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1.png (7.4 KiB)
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Up to 10 attachments (including images) can be used with a maximum of 3.0 MiB each and 30.0 MiB total.

Thanks Jeff, I will test with Outlook in safe mode, although I do not believe that I have any add-ins. My Outlook version is: 16.0.13462.20352. The version is managed by my system administrator. The option for "Don't download pictures..." was already not checked. This problem seems to happen only after having outlook open for a few days. I will take a screenshot of it next time.

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78303-blank-img-tag.png



It still occurs with safe mode enabled.

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blank-img-tag.png (2.7 KiB)

Hi @DarrenBraynard-0686,
Thanks for your updates.
Personally I think, considering that those images can be displayed normally for a while, we might could try troubleshooting from the perspective of mail image cache. It is suggested for you to try empty the OutlookSecureTempFolder or assign a new valid folder path for it to see if the issue could be resolved. For more information, please check: Pictures cannot be displayed and are shown as red X in Outlook.

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Hi @DarrenBraynard-0686,
Just checking in to see if above information was helpful. If you have any further updates on this issue, please feel free to post back.

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I checked and this was the value for version 16.0. This folder did not exist on my machine. I made it point to c:\temp0 as suggested in the instructions. I'll let you know if it happens again. Thanks.

C:\Users\Darren Braynard\AppData\Local\Microsoft\Windows\INetCache\Content.Outlook\ZTQI5B2N\

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Also, the following folder didn't have Content.Outlook, but Content.MSO instead. It has some random images that look like they might be from emails of mine. Is this the new replacement folder for outlook caching?

C:\Users\Darren Braynard\AppData\Local\Microsoft\Windows\INetCache

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The issue still persists. I set the OutlookSecureTempFolder to a new location C:\temp0 earlier today. Just now, the base64 img tags have suddenly showing black squares again.

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Hi @DarrenBraynard-0686,
Thanks for your updates again, though I still could not get much useful information yet. Sorry for my delay. I'm trying to do the same tests on more different devices and see if the issue has any difference. Can your issue be reproduced on other devices in your environment? And how long is specific "over time" before the issue occurs? If you got more tests and useful information, it would be so nice that you could share with us here.

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After restarting outlook it could be as little as 30 minutes or as long as a few hours. I will forward these emails to a coworker to see if the issue replicates on their account.

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