How to Underline in a Plain Text Email Messages

Not as Pretty as HTML, but Easy

HTML vs Plain Text

The majority of emails we send are HTML-based. HTML stands for HyperText Markup Language. It’s the way web pages are encoded to handle things like bolditalics and text color. It includes ways to specify formatting, colors, positioning, and some amount of layout. As email became more popular, people started wanting to make their messages “look” as nice as they felt web pages looked.


Plain text is as if the email was written on a typewriter, which means no formatting, no images, no pretty fonts, no hyperlinks. It’s often displayed using what’s called a “mono-spaced” font – meaning that each character takes up the same space on the line. While they may not be nearly as attractive as HTML-based emails, plain text emails play a significant role in a well-rounded email marketing strategy. In fact, in the testing done by Hubspot, plain text email had a higher open and click rate than HTM, every time.

And while plain text may be plain, it's more likely to be readable on devices like the Apple Watch.

HTML, Plain Text and MIME

Most emails composed by humans, and this article assumes the reader is human, are sent via SMTP in MIME format (Multipurpose Internet Mail Extensions).That means that a plain text version of your email is bundled along with the HTML version of your email.

Unless you’re sending out a solely plain text email, multi-part MIME should be part of every email campaign because spam filters like finding a plain text alternative and some people prefer it.

How to Underline in Plain Text Email Messages

If you use HTML formatting, you can underline as much as you like (which should not be too much if you like your messages easy to read).

If you write your email in plain text, you can still underline as much as you like, and everything remains perfectly legible.

To mimic underlining in plain text email: Use underscore characters at the beginning and end of the _underlined passage_.

Alternatively, you can also use bold face to emphasize in plain text emails or use italics.