When a recipient forwards your email message, it's the email client that's responsible for the HTML rendering. So it's not your ESP or sending platform. Some email clients (such as Outlook) may not render the HTML correctly, which is a known limitation in email marketing.
This can include stripping out certain HTML elements, wrapping your email in a blockquote, or inserting extra lines of code. All of which can break your design and make the email less functional for the recipient of the forwarded email.
There is very little we can do to completely avoid changes to your design when a subscriber clicks on the forward or reply button.
What should you do when a forwarded email breaks?
Here's the bad news first: it's impossible to completely avoid that your email changes once forwarded. Whether an email client alters your code isn’t something you can control.
Yet, there are some workarounds you can take to optimize your emails.
- Keep your email design simple. While it doesn’t work for everyone, simpler layouts (e.g. single-column) typically hold up a little better when forwarded. If your email is less complex, there is less that can go wrong.
- If your ESP has a forward to a friend feature, you can add the forward to a friend link in your email message. For example, here's how it works in Mailchimp.
Hope this helps! Let us know if you have any questions.