Newsletters should include a text version as well, and you can set your client to show that instead of the HTML.
"Normal" users (i.e. the non-geeks) do seem to prefer HTML emails, and in usability studies, A/B testing, and deliverability reports, HTML emails usually outperform text.
In short, HTML emails are better for and preferred by recipients and senders in all but edge cases.
I find that sadly, more and more HTML email does not include a plain text part. I realize I'm in in a small minority of people who don't use a graphical email app. But if you care about that at all (and you probably should so that you also make life easier for your visually impaired clients who use screen readers) you should include plain text. Otherwise I simply won't read the email that you spent so much time and effort painstakingly formatting.
Look, it's all well and good to say "I'm 1337! I use Mutt, or I use Links!". But let's be honest, the majority of people are not going to use a text mode web browser or a text mode email client.
And this isn't something you're born with, like a vision impairment, so people need to make a website accessible for you. This is a personal preference.
Hence, as much as some of us neckbeards might like to go back to a works where 256 colours was the bomb =), the rest of the world has moved on.
Text only e-mail is more productive for everyone, in exactly the same way that text only authoring applications are more productive. When you are writing something, fiddling around with the layout is just a distraction. Many people might prefer it, but lots of people also like to play Patience on their workstation rather that getting on with what they are supposed to be doing.
I have been a text-email lover and html-email hater until early this year (2013). I realize that almost everyone neither have any clue of the difference nor do they care. As mentioned elsewhere in this comment thread, people do love beautiful emails - the html kind.
I have dealt with quite a bit of clients and they love to use colors as separation for various degree and scaffolds of conversations.
For now, if I'm initiating an email and do not really need to be HTML, I try to stay with text. For other, I just follow the format the current email thread is in.
If your goal is to distract and confuse people, by getting them to click on your ads and buy your products, then use HTML e-mail. If you want to communicate clearly, then stop worrying about layout & typography and concentrate on the words you are writing.
Because the vast majority of people enjoy pretty emails with non-monospaced fonts, whitespace and colors. It's mostly hackers who want to show off how old school they are that complain about html emails. Also, most emails like this have a text version you can receive - I believe it's necessary for CANSPAM compliance.
I very much prefer for emails to contain text only, or with HTML only as attachments, and it has absolutely zero to do with any desire to show off to other people.
For me, it's all about keeping some control over technology. I tell a very limited program like mutt what to do, and it does it. This is in contrast to begging an incredibly complicated program like a browser to do something, where much of what it is doing is controlled by invisible embedded code written by people who may be hostile toward me.
I spent some years working at an email-specific agency. They sent more than 5 billion emails during that time for some very big clients, and we did most of the data analysis. They also did a lot of usability testing.
I can tell you that on just about every metric - brand recall, clickthrough rates, ROI, unsubscribes - HTML outperformed plain text. There were exceptions, both in terms of types of campaign and types of sender - say, if your list includes lots of Hacker News readers.
Ok, I am aware of the higher click rates, but that is part of my point. Well crafted imagery is no doubt more catchy and attention getting than plain text. However, is visual stimulation (manipulation?) supposed to be a part of communication medium? Between the reasons for why HTML should be in emails, where do you rank recipients well-being compared to ROI?
I don't think anyone is better off getting graphics and colors in their email, even if they enjoy it. After all, the email is supposed to inform of something. A website can be an interactive app, but email?
Also, text-only doesn't mean monospace. I'm happy to read email in whatever sans-serif font the email client picks, with nice whitespacing.
Fortunately, most e-mail clients support a "show this e-mail in text only" view mode. This means that you can have it your way, and others can have it theirs!
The problem is that "show this E-mail in text only" relies on the fact that whatever they use send out the E-mail also sends plain text as well as HTML as a multipart. I find most of places do that, but there are some services/implementations that simply sends out HTML, pretty much leaving it up to the mailer to interpret that E-mail.
Either you will be sending in HTML or plain text, I feel there shouldn't be any excuse of not attaching plain text version of it.
"Normal" users (i.e. the non-geeks) do seem to prefer HTML emails, and in usability studies, A/B testing, and deliverability reports, HTML emails usually outperform text.
In short, HTML emails are better for and preferred by recipients and senders in all but edge cases.