It can be hard to create an email that displays identically across all email clients, so you might be tempted to create one large image so that every person sees the same text, fonts, and images. However, there are several reasons why doing this might affect your email delivery rates:

• Email clients may flag your messages as spam: Because email clients aren't able to parse text contained in an image, many spammers use this technique to bypass spam filters. You run the risk of getting your messages flagged as spam if you send an image-only email.
• Your emails require multiple clicks to view: Some email clients hide images until the user opts to display them. While adding an extra click may not seem like a big deal, this can result in a significant decrease in the number of people who end up viewing your message.
• Your emails aren't searchable: In the event that a user saves your message, he or she won't be able to use the search function to find it at a later date. This makes it hard for people to reference the information you've sent.
• Your emails may not even load: For users on slower connections (such as mobile users), your image may not load. If it does, it may not load before the user navigates away from the email.

All of these consequences have a negative impact on the conversion rates of your website--if the user doesn't see your email, he or she cannot interact and engage with your content the way you want.

Use HTML-based Emails Instead of Image-Only Emails

When you send HTML-based emails containing mobile-friendly features, you increase the number of people who can read your emails. This means that it's easier for them to take action--higher click-through rates on your emails directly correlate to higher conversion rates on your website.

While including mobile-friendly features (especially when you take into consideration the needs of all the different email clients available) requires you to spend more time ensuring that your HTML works as desired, the consequences of using images instead are too high to ignore.