What’s the role of text version fallback in deliverability?

Most email clients render HTML beautifully. But your email doesn't always travel the clean path from send to inbox. Security gateways, accessibility tools, screen readers, and a handful of email clients that still prefer plain text all interact with your message before a human ever sees it. Some of them only look at the text part.

Here's what's actually happening under the hood. When you send an HTML email, your ESP wraps it in a MIME multipart/alternative structure. That's two versions of your email bundled together: an HTML part and a plain text part. The receiving client picks whichever format it can handle. If no text part exists, systems that expect one will either see nothing or generate a red flag.

Spam filters pay attention to this. A missing text version (or one filled with junk like "View this email in your browser" and nothing else) can nudge a filter toward suspicion. Spammers typically skip the text part entirely or populate it with garbage. A real, readable plain text version signals that a real person put thought into this email. It won't save a bad sender, but it's a genuine quality marker for filters that check.

The text version should actually work as a standalone message. Don't just strip the HTML tags and call it done. That produces a mess of broken links and orphaned words. Instead, rewrite it for linear reading. Keep the important links (written out in full, like https://captain@deepcurrent.io/orders), summarize the content clearly, and make sure it makes sense without any visual layout.

It also helps with accessibility. Screen readers and some assistive tools pull the text part directly. If it's thin or missing, you've made your email harder for those readers to use. That's worth caring about even beyond deliverability. (See how WCAG standards apply to email for the bigger picture.)

Most modern ESPs handle the multipart structure automatically, but they rely on you to actually write the text version. Don't leave it blank. Don't auto-generate it from stripped HTML. Take two extra minutes and write a clean version. It's one of those small things that quietly adds up to a healthier sending reputation over time.