My Customer Received an Email That Looks Like Code

This rare issue may occur with emails at,, and some other very old email systems. Read more here.

The Problem

One of your recipients has received an email sent by Fuse but instead of the beautiful content you created, they received a mess of jumbled code.

The Reason

Much like websites, Emails are creating and sent using web code. As new innovations are made, new code becomes possible.  Some new developments never stick, while others have the potential of being implemented with various competing forms of code.  

The World Wide Web Consortium (also known as W3C) is the primary body responsible for setting web coding standards so that all web-based services (including email providers) can successfully communicate and display the appropriate content. The vast majority of web-based services conform as closely as possible to W3C standards or risk getting left behind.

As the W3C sets new standards for web and email coding over time, it is the responsibility of companies that provide these services to update their systems accordingly.

How Fuse Avoids the Problem

Our email is generated using the best and most current web standards to ensure the best possible experience for the largest majority of recipients.

Why & Where the Problem Still Occurs

We have no control or influence over the ability of any outside email service to keep their programming up-to-date with modern standards.

Unfortunately, there are still some email services in use that have fallen behind on this matter.

For example, users of and have encountered repeated display problems, particularly when they read their incoming email using a separate email inbox tool (such as Outlook, etc.) to which their optonline or optimum email is automatically forwarded.  Under these conditions, optonline and optimum appear to be using very old (estimated 13 years old) email rendering code which results in an email that looks like a large mess of code instead of the carefully-designed message you intended to send.

We have investigated this issue in-depth and determined that, sadly, there is nothing we can do to resolve the problem.  It will only be resolved if and when the provider of optonline and optimum email addresses chooses to update/improve their rendering/forwarding code to conform with more up-to-date standards.  Based on our attempts to reach out to the company, it appears that the creator of their rendering code went out of business 13 years ago so we can't currently predict if or when it may ever change.

What you can do

For most agencies or brokers, optonline and optimum addresses are only a small portion of your total email list. Out of those, we can't be sure how many of them read their email in a 3rd party inbox tool vs. simply using optimum's online email reader (which we've tested and confirmed is rendering correctly!).

In other words, the portion of potential recipients affected will be quite small if not insignificant for most agencies and brokers.

If this is a concern for you, one option is to simply avoid emailing any email address at these domains.  You can do so in a couple of different ways:

  • Option 1: Every time you send a manual message or set up a campaign, make sure you filter your recipients by using a segment that excludes all Accounts where the Account > Email contains or

  • Option 2: This option is a bit more extreme but if desired you can completely exclude all Accounts with optimum/optonline addresses from importing to Fuse. This can be done by navigating to Exclusion Rules from your List Setup page.

Please Note: Optonline/Optimum are used as examples here because they still have a fairly large user base in some parts of North America.  Other email services with outdated rendering code tend to have extremely small/insignificant user bases or are out of business, so this issue is very rare outside of these 2 example domains.  

If you happen to have a customer with a different email domain who is experiencing this same issue, we recommend simply unsubscribing them or even better recommend that they sign up with a new email service.

If everyone you have emailed is experiencing this issue, despite having addresses at various domains, please notify our support team right away!