We were going to start sending email campaigns in production and discovered that in EXM if we go into a message tab the Preview does not work. It just shows An internal error has occurred. This is happening with our custom base email template, as well as the out of the box sample newsletter.

Using Sitecore 9.1.1, SXA 1.8.1.

There is nothing obvious as to what the internal error is in the log files or in application insights. I also tried using fiddler but the response of the failed request just has the same message as appears in the body field below.

All other environments are fine - it's just production. I have checked all the things published (templates, renderings, email root).

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If you click into the body the Experience Editor loads fine with the modules all ok. Saving and closing just leave it in an error state on this screen and in the Content editor preview tab.


Have discovered that accessing this CSS file is erroring:


Although still unsure why this file is not accessible via web browser.

  • Check EXM and Sitecore logs. Usually there you will find more details Nov 19, 2019 at 9:30
  • @PeterProcházka checked them - nothing found when the error occurs. We have our EXM configured to log to application insights where I've checked traces and exceptions. The general log file also has nothing. It's like the exception is being swallowed or potentially there's something specific I should be searching for in the log file that I'm missing.
    – Jen
    Nov 20, 2019 at 3:17
  • @PeterProcházka Seems to be a problematic CSS in Azure. :|
    – Jen
    Nov 20, 2019 at 5:19

1 Answer 1


This turned out to be caused by a handler added as part of the Sitecore recommended security practices outlined here.

Adding the following line to the root Web.config as per the Security Tasks was the cause:

<add path="*.xml" verb="*" type="System.Web.HttpForbiddenHandler" name="xml (integrated)" preCondition="integratedMode"/>

Turning on errorMode="Detailed" in the httpErrors section of Web.config (see below) showed a duplicate key with the same entry in the \sitecore modules\Shell\EmailCampaign\web.config file which caused an HTTP 500.19 error.

    <httpErrors errorMode="Detailed"></httpErrors>

Commenting out the handler in the EmailCampaign\web.config fixed the problem.

  • 1
    Unfortunately, this handler is enabled by default when installing Sitecore 10.2, causing EXM preview to break with a vanilla installation. Jul 7, 2022 at 13:06

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