Investigating Email Guardian alerts

Email Guardian automatically scans your selected emails every 24 hours for unexpected issues caused by email client updates and other external factors and checks for broken links that affect your content. Email Guardian notifies you of any changes that might impact your subscribers’ experience.

NOTE: It may take up to 24 hours for the new version of your email to be reflected in Email Guardian.


Email client monitoring

Email client monitoring uses a custom comparison algorithm that is designed to detect substantive rendering differences while ignoring irrelevant differences such as antialiasing artifacts. Litmus calibrates the threshold changes on an ongoing, per-client basis. While we can't share exactly how we determine if an issue should be alerted to (that is our secret sauce!) a few examples of changes we might detect are:

A change might include changes like:

  • A medium-to-large image fails to load.
  • Image loading failures that cause a noticeable shift in the layout of the email.
  • Changes by the email client in the availability or functionality of an HTML/CSS feature, that affects rendering throughout the email.
  • A font change is visible across the majority of the email.

Image and link monitoring

Both image and link monitoring either pass or fail, due to this any alert (outside of loading speed) will be considered an impact and you will receive an email notification.

NOTE: If your email has dynamic images, it could trigger an Email Guardian notification. If this is the only change you see, dismiss the alert with the corresponding dropdown option.

View monitored emails

To view alerts for a monitored email, hover over the email you want to view and click the monitor tab. If you haven't turned on email monitoring please see how to set up email monitoring.

Litmus inbox with Monitor and other buttons in view

From the monitor tab, you will see a list of all of your monitored email clients and links. Any impacts for email clients or links will be at the top.

Email with Monitor pane open on the right showing alerts and impacts

Email client monitoring

View an email client alert

Any changes detected to your email rendering will show up in the email clients section of the monitoring tab. To view further details, click the email client you want to view.

Each email client will have a detailed page where you can investigate the change. From here, you can view the Previews & QA test, investigate the changes, or dismiss the alert.

To view changes, use the red slider to compare your original email rendering to the most current one. You will see the baseline screenshot on the left, with the most recent capture on the right.

Animation of red slider moving to show original on left and changes on right

If you want to see a history of changes spanning the past 14 days for your email, click the View history link in the banner at the top of the preview window.

Email Guardian alert banner with View history link at the right

This will bring you to a record of scans on your email and if any changes have been detected.

Email Guardian history showing all checks for an email client

Link monitoring will monitor your links to verify that your links are valid. If we detect a broken link, we will alert you with an email notification. You can view the links we are monitoring in the monitor tab.

When a subscriber clicks a link, that request is sent to the website where your content is hosted. If the website can't return the content to a subscriber through the link provided, the hosted website will communicate using status codes. Numerous codes can indicate client-side errors which you can take back to your IT team or whoever manages the website where your content is hosted.

NOTE: In most cases, Link Monitoring will be able to monitor the status of dynamic links as long as we have a version of the email that’s the same as a subscriber would receive it. 

View a broken link alert

Each link location in your email will be marked with a blue link badge to indicate the link is working. Red links will have a red link badge to indicate the link is no longer working as it should. A grey link badge means we don't monitor that link and the link has been skipped.

Email guardian link monitoring pane on the right with link pin icons in the email preview

To view further details of the link, click the link in the sidebar to view a detailed breakdown of the URL, redirects, destination link, and loading time.

Animation showing results of a link alert

How to copy link details to share with others

To share this information with others, you can use the copy to clipboard action which will provide a snippet with the following information:

Link Content: update your profile
Link URL:
Redirect Count: 1
HTTP Status Code: 200
Total Load Time: 1908

Dismiss a broken link

If you find a link that has been flagged but works as expected, you can dismiss the alert and tell Email Guardian to ignore the link. Please note, this can not be undone.

Options to copy alert information or ignore it at bottom of alert pane

Image monitoring

View a broken image alert

Each image location in your email will be marked with a blue image badge to indicate the image is working. Broken images will have a red badge to indicate the image is no longer working as it should.

To view further details, click the image to view the image summary. The image summary will include the Image Name, Image URL, Destination (if redirects are involved), Image Alt Text, Image Size, Image Load Time, and an error Response Code if applicable.

Images with long loading times

Images with a "!" icon indicate a long loading time. We flag images that take longer than 6 seconds to load and recommend optimizing them for faster browsing experiences.

Embedded images in image monitor

Embedded images are image files uploaded directly within an email. We do not check embedded images at this time. Embedded images will show a grey state image icon, indicating we are not monitoring. You will only be able to see the Alt Text and Image Size in the image summary.

Note: In addition to inconsistent support in inboxes, embedded images increase the overall size of an email which may affect loading time, engagement, and more.  We encourage you to host images on your own server or through your Email Service Provider using absolute links (no relative links).

Both image and link alerts will show an error code indicating the response from the website of the link destination or where the image is hosted. The communication status codes will have a corresponding message. Numerous codes can indicate client-side errors which you can take back to your IT team or whoever manages the website where your content is hosted.

Server was too slow to respond

The request to load a web page took longer than the website's server could wait so the connection with the website "timed out." The most common cause of this error is an incorrect URL. It could also be caused by a slow connection or connectivity issues. Please make sure the URL provided is correct.

We could not complete the request

This error happens when the server detects too many attempts to access your website within a short period. This can either be due to a user trying to log in with the wrong credentials or too much traffic to your website. Whenever this situation occurs, the system will activate a rate-limiting feature, triggering an error. Rate limiting is a strategy used to limit network traffic when it detects an excess of activity. Check with your web domain hosts to see what the limits are and verify it can support the network traffic to your site.

Server encountered an error while responding

Server errors occur when something goes wrong on the server while your request is being processed. This error message can occur for a variety of reasons. Verify that the link is correct and that the server can handle incoming requests.

Server denied the request

This is an error message that might occur when a user is trying to access your website or a specific web page they don't have access to (maybe it requires a login or is behind a firewall). This message indicates that the web server the user is trying to connect to has refused the request to access. Make sure the webpage you are linking to is accessible to the intended users.

Path could not be found.

This is a common error when a user attempts to follow a broken or dead link to a webpage that can't be found. Verify the link is correct.

SSL certificate error

An SSL certificate error occurs when a web browser can't verify the SSL certificate installed on a site. Rather than connect users to your website, the browser will display an error message, warning users that the site may be insecure. An SSL is a digital certificate that authenticates a website's identity and enables an encrypted connection between the user and your site. Reach out to where your domain is hosted to add a certificate to your site.

Domain name not found

When you receive this error message, the IP address that matches the website domain name you entered can not be found. There are several reasons why a DNS domain name resolution might fail. One of the more common reasons is that the DNS server is (temporarily) unavailable. Verify your hosting domain is set up properly.

Email address format not valid

The email address is not valid, please make sure the email format is correct.

Telephone format not valid

The format must start with a number or a + (to include country code). Phone numbers must only contain digits, dashes, periods, or spaces but no alphabetical characters or other punctuation like !, #, $ etc.


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