Multipart Alternative Format

Why MIME Content Type is Widely Used in Email Marketing and Should You Use it Too?

If you’re subscribed to at least few newsletters online, then there’s a big chance that they use plain text format. The reason why so many ezines and newsletters online use text, instead of HTML is that publishers are afraid that their readers with older mail clients won’t be able to read HTML messages. So they stick to plain text. However, there’s a solution to this problems. It’s called “multipart alternative”.

Multipart alternative is a specific content type that is used when sending emails. This simply means that the email that a publisher sends is delivered in two formats (HTML and plain text). If reader’s email client can’t read HTML emails, it shows reader plain text version of the message. If reader’s email client is able to read HTML then it delivers HTML. Sounds good and simple right? Yes, but there’s actually a problem with this too.

If your email client cannot determine multipart alternative content type, it gives reader a choice to read both. That means people will see both ugly formatted HTML and text versions of your message. Of course, this is rare case, but it still might happen. So the thing to remember here is that you should send text part of the alternative multipart message first and the HTML part second. This way, older email clients will not see unreadable HTML decoded hieroglyphs, but will be able to see a simple text first.

How MIME Type Looks Like?

The first part of the multipart alternative email looks like this:

Content-Type: multipart/alternative;
boundary="Multipart Boundary 5061580520"

The line above tells email client that this message is mixed and it uses two versions, plain and HTML. The boundary can be actually different in various messages.

Then there’s a plain text part in the email that represents the text version of the message:

--=Multipart Boundary 5061580520
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit


...here goes plain text version of the message...

The first part of content type is plain text. This is seen by older browsers if they can’t read HTML.

The second part of boundary and content type is HTML:

--=Multipart Boundary 5061580520
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit

...<h1>here goes HTML version of the message</h1>...

If the email client is capable of reading HTML messages, then it skips the first boundary and goes right to the second part – HTML.

Managing Two Lists

As you can see, multipart alternative has some disadvantages and if you want to be absolutely 100% sure that your clients will get the correct messages, then you might think of managing two newsletters. One HTML and the other plain text.

You could send out HTML message to clients that signed up for HTML newsletter. And then send out plain text email to another list that subscribed to receive text version of your newsletter. Of course this is time consuming, but then you’d be sure that your readers won’t get cluttered messages as it might happen using multipart alternative format. Besides, your messages will be shorter.

Using alternative multipart function you send out two (HTML and text) messages to your readers. If your text message’s size is15kb in plain text, then it might easily become 45kb in HTML format. That means you’re sending 60kb to every subscriber. If you have 1000 text and 1000 HTML subscribers, then you’re wasting a bandwidth by delivering unnecessary parts of the message to your readers. If your host doesn’t give you enough monthly data transfer, you might get in trouble quickly.

In Conclusion

Multipart alternative is a great way of delivering both HTML and plain text versions of a message and satisfying your readers. The only problem is that some old email clients do not display your message correctly if they can’t understand which version to deliver. However, such old clients are very rare these days. Most of the people are using modern email clients and should be able to read your multipart messages.

Most mailing list or autoresponder software or services also offer the ability to send multipart alternative messages to your visitors. So if you’ve decided that providing two versions of the message to your visitors is a great way, then you can start using multipart alternative in your emails right now.