Each email you send actually includes two versions - the HTML with its stylish images and formatting, and the plaintext with its, well, plain text. While creating a mailing using the content editor, you'll be able to view them both. Before you send, you'll always want to double-check both versions to make sure they look just the way you want them to.
When you send, the two versions form a multi-part message, and your recipients' mail clients simply display the version they prefer. As you know, most will display the HTML, and some will keep it old-school and display text. Your plaintext crowd includes folks who use HTML-disabled hand-held devices, folks who've set their email clients to show text, and folks who work at companies with a strict no-HTML policy, to go along with the other office policies of: 2. no tanktops, 3. no open-toed sandals, and 4. no hitting coworkers with your open-toed sandals, which you shouldn't be wearing anyway had you carefully read rule number 3.
So how is it that someone might receive the plaintext version over its more attractive, confident HTML sibling? Here's how:
In this case, either the recipient has turned HTML off for incoming emails, or someone at their company or email host has. When your email arrives, the plaintext is the one that makes it through, and the recipient may view the HTML in all its glory by clicking the view-this-online option at the top of most mailings sent through your account.
Though the HTML-or-text decision happens on its own, you can also let your recipients pick their own format when they sign up. Start by turning on the email format field inside your audience records (open any record and use the 'add more fields' option). Then hop, or perhaps skip lightly, over to your signup form and add the format field as an option there. Your recipients can now hard-set their format when they sign up or whenever they manage their preferences.
When someone signs up to get your emails (and does it using your account-provided signup form), we send them a quick confirmation note. It's an email you can personalize, and it's sent in plaintext form as a quick way to welcome your newest subscriber and make sure he or she adds you to the all-important address books or safe senders lists before your real mailings begin arriving. (Of course, you can turn this confirmation email off, should you decide you'd like to create an automated welcome email in its place.)
Most of your emails will be delivered (and accepted by the receiving hosts) on the first pass. But some won't -- either because an inbox is full, or a server is down or simply not responding. If at first we don't succeed, we try, try again, sometimes up to 30 hours after you hit send. (We label those re-tries emails in progress on your Response page.)
During one of those follow-up delivery attempts, we strip the email down and try sending a plaintext version. Why? To make sure a server isn't rejecting it simply because it spots an HTML version (as silly as it sounds, a few filtering programs do just that). If the plaintext email does make it through, we automatically flip that audience member's preference to plaintext for future emails. That's why someone might begin receiving plaintext emails even if no one has set his or her preference to plaintext -- it's just us trying to deliver as many of your emails as possible.
Can you set someone's format preference back to HTML? You bet. First, do a quick search and find that person's member record. Using the 'add more fields' option at the bottom, add the email format field. It will be set to 'text,' and you can just switch that to HTML and save.
Oh, and whether or not you plan to let your recipients make their own choices, it's a good idea to turn the email format field on in your account; that way, you can quickly see what someone's format is and adjust it any time you need to.
Can you set someone's format preference to Klingon? Only if you're sending to recipients in the Star Trek universe. If you are, how's your open rate?