The entire message says something like this:

In order to fix this issue, you need to disable the option that prevents Outlook from downloading pictures automatically in standard HTML email. There are three ways to do that – using in-built options, Local Group Policy Editor, and Registry Editor.

Do you want to download external content – Outlook

To fix Do you want to download external content message error in Outlook, follow these steps: To learn more about these steps, continue reading.

1] Enable automatic picture download using Trust Center

To enable automatic picture download using Trust Center or in-built setting, follow these steps:

Open Outlook on your computer.Click on File > Options to open the Outlook Options panel.Switch to the Trust Center tab.Click the Trust Center Settings button.Go to the Automatic Download tab.Remove the tick from Don’t download pictures automatically in standard HTML email messages or RSS items checkbox.Remove the tick from the Don’t download pictures in encrypted or signed HTML email messages checkbox.Click the OK button.

Then, you should not find any issues anymore.

2] Turn on automatic picture download using Group Policy

To turn on automatic picture download using Local Group Policy Editor, follow these steps:

Press Win+R to open the Run prompt.Type gpedit.msc and hit the Enter button.Navigate to this path: User Configuration > Administrative Templates > Microsoft Outlook 2016 > Security > Automatic Picture Download Settings.Double-click on the Do not permit download of content from safe zones setting.Choose the Disabled option.Click the OK button.Double-click on the Automatically download content for e-mail from people in Safe Senders and Safe Recipients Lists setting.Choose the Enabled option.Click the OK button.

Then, close all windows and restart the Outlook app. Hopefully, you won’t find the issue anymore.

3] Allow downloading pictures automatically using Registry

To allow downloading pictures automatically using Registry Editor, follow these steps:

Press Win+R > type regedit > hit the Enter button.Click the Yes option in the UAC prompt.Navigate to this path: HKEY_CURRENT_USER\Software\Policies\Microsoft\office\16.0Right-click on 16.0 > New > Key and name it as outlook.Right-click on outlook > New > Key and set the name as options.Right-click on options > New > Key and name it as mail.Right-click on mail > New > DWORD (32-bit) Value.Name it as unblocksafezone.Create another REG_DWORD value and set the name as unblockspecificsenders.Double-click on each of them and set the Value data as 1.Click the OK button and restart your computer.

Then, you can open the Outlook app without any errors.

Read: The operation failed because of a registry or installation problem – Outlook

What is external content in Outlook?

External content denotes the pictures and other elements that are included in an HTML email and need to be downloaded from another server. As these things need to come from a third-party server, it justifies the name, external content. An email can contain external images and iframe.

How do I download content from Outlook?

To save an attachment from Outlook, you need to open the email first. Then, find the attachment and click the arrow icon. Here you can find one of the two options – Download, Save As. You can click on either option to save or download the content from Outlook. That’s all! Hope these guides helped. Read: The file cannot be opened message in Outlook – Outlook Data File.