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Reach More People and Improve Your Spam Score: Why Multi-Part Email is Important


While plain text emails may not be as flashy or attractive as HTML emails, multi-part emails are a critical component of a well-rounded marketing strategy. Plain text emails are not only a great option for transactional emails, but they also serve as excellent templates for crisis communications. Most importantly, the plain-text portion of an email message serves as a back up in situations where your subscriber’s preferences or email client capabilities cannot support viewing HTML.


Multi-part MIME (Multipurpose Internet Mail Extensions) bundle together a simplified plain text version of your email along with the HTML version of your email. While the HTML version of an email message can contain colors, graphics, specific fonts and links, the plain text part is well, plain. Your formatting options are limited to title case, sentence case, all caps and basic symbols (although we have seen some impressive examples of ASCII art in plain text emails).

As Tom Burke explains,

A multi-part MIME message is like a package with multiple boxes within it. In your standard HTML + text message, both types of content are sent in the email. Your email client, assuming it understands MIME format, will decide which of the boxes to open and display to you.

Email clients will not show both the HTML and plain text parts of an email message to the subscriber simultaneously. Rather, the subscriber’s email client will display the version that corresponds to the subscriber’s preferences and the capabilities of the mail client itself. Since most modern email clients support at least basic HTML, the HTML version is usually shown. However, if subscribers have changed the settings or preferences in their email client to receive plain text emails, the mail client will honor that desire. As shocking as it may seem to email lovers like ourselves, some people prefer to receive plain text emails over HTML (and others believe that HTML has no business in email at all).


HTML version


Plain-text version

Behind the scenes, the MIME protocol allows a sender to break down the HTML and plain text parts of an email in the header. In this case, we’re referring to the part of the message that helps route your email to the proper location rather than the visual header that might contain a logo, navigation or other branding. As eNewsletterPro explains, “MIME allows you to define multiple parts of an email using the Content-Type header.” In the example below from eNewsletter Pro, you can see how the message is divided into specific sections:

  • The plain text portion follows the Content-Type: text/plain header, and is highlighted in blue
  • The HTML portion follows the Content-Type: text/html  header, and is highlighted in green
X-sender: <>
X-receiver: <>
From: "Senders Name" <>
To: "Recipient Name" <>
Message-ID: <>
Date: Sat, 24 Sep 2005 15:06:49 -0400
Subject: Sample Multi-Part

MIME-Version: 1.0
Content-Type: multipart/alternative;


Content-type: text/plain; charset=iso-8859-1

Content-Transfer-Encoding: quoted-printable

Sample Text Content


Content-type: text/html; charset=iso-8859-1

Content-Transfer-Encoding: quoted-printable





<div style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Sample HTML =






Unless you are sending out a solely plain text email, multi-part MIME should be part of every email campaign. HubSpot has put together some great reasons why sending in multi-part MIME is a necessity:

  1. Some email clients and devices cannot handle HTML: As we explain in our infographic, “The Road to Rendering,” a variety of factors can impact the ability of email clients and devices to support or display HTML properly. For example, some BlackBerry devices (such as the Blackberry OS 4 for Blackberry 8900) don’t support HTML email, so the plain text version will render instead. However, if you do not have a plain text alternative, the HTML code will show up in your subscriber’s inbox instead—not ideal!
  2. Some people simply prefer it! As we mentioned above, some people just prefer plain text emails, and some email clients give users the option to receive only the plain text version. If your subscribers have enabled this setting and you’re only sending an HTML version, your email may not reach these subscribers!
  3. Spam filters like to see a plain text alternative: A lazy spammer wouldn’t take the time to create a plain text alternative, so HTML-only emails are a red flag for spam filters!


Most Email Service Providers (ESPs) will send in multi-part MIME automatically, or walk you through setting it up as an option. They might have a tab or section during the email setup process that asks you to create the “plain text” version of an email. In addition, they handle packaging it up, adding the appropriate headers, and sending it out to subscribers, so you don’t need to worry about it! Here are a few examples:

Campaign Monitor






If you’re not using an ESP, you’ll need someone to set up the headers manually, which shouldn’t be too difficult for anyone with programming skills. Cullin Wible explains, “From a technical perspective, composing a multi-part message is much easier than coding HTML content itself.” The code should be contained in the header of the email and is only visible if the source of the email is viewed.

Here is a great resource on manually setting up multi-part MIME messages:

Litmus Spam Testing

Multi-part MIME messages are only part of the picture. Identify issues that might keep you from the inbox and get actionable help for how to fix them with Litmus Spam Testing.

Start testing now →