Is plain text just plain best?

I have a colleague who regularly uses email to prospect for consulting work. She sends out plain text emails, and swears by the results.

Every now and then the 'text vs HTML' debate is re-kindled. Just when is it best to send in plain text?

Let's consider the benefits:

• no worries about rendering or image blocking
  
• good delivery rate: less likely to fall foul of filters
  
• may be more likely to get read, doesn't look like a 'marketing email'
  
• the 'low tech' approach may be better received by some target audiences

But what are the cons? Here's what comes to mind:

• no way of tracking opens
  
• trackable links can be very long and in some email clients this will cause them to break
  
• with no graphical content the copy has to be excellent
  
• for some businesses the images are crucial (eg mail order clothing)
  
• lack of visual branding may make the message unmemorable

My consultant colleague only sends out small numbers of highly targeted emails, and I would guess her high success rate is down to relevance and timing, two of the most important factors in any email campaign.

For the majority of clients I still recommend HTML, but with the usual caveats: don't rely too heavily on images, include a link to a web version, offer a plain text version for those who prefer it and send your campaigns in multipart format, so that the text version is delivered if HTML can't be displayed.