ficd.sh/content/blog/email-formatting.md

---
title: Email Formatting Is Harder Than It Looks
date: 2025-07-14
---

*[UTF-8]: Unicode Transformation Format – 8 bit. Text encoding standard.

*[plain–text]: Content representing only readable characters, and whitespace characters that affect the arrangement of the text.

[Kakoune]: https://kakoune.org

[^html]: The first email was sent in 1971 --- HTML was specified in 1990.

[TOC]

## Plain text email

As I've [mentioned before](./email-in-kakoune.md), I like using [Kakoune] for
reading & writing emails. Of course, Kakoune a source code editor, not a _rich
text_ editor. It operates on UTF-8 _plain–text_ --- which means that the emails
I write need to be in plain text, too.

As it turns out, plain-text email (which predates HTML by decades[^html]) hasn't
really left a "legacy" so much as it _hasn't actually gone anywhere_. Many
developers swear by it; some are even so committed as to automatically filter
`text/html` mail as spam. If you want to learn more, you can begin by reading
[Drew DeVault's post](https://drewdevault.com/2016/04/11/Please-use-text-plain-for-emails.html),
[useplaintext.email](https://useplaintext.email/#why-plaintext), and sourcehut's
[mailing list etiquette](https://man.sr.ht/lists.sr.ht/etiquette.md) guide.

As I went down `text/plain` path, I quickly learned that I needed an **email
formatter**. Why? Plain text is like source code. You can't rely on the
recipient's mail client to render it in a certain way --- you have to assume
that what you see is _exactly_ what _they_ get.

On one hand, this isn't really a problem --- the whole point of plain text is
_not_ having to bother with formatting, right? There is, however, a crucial
catch: **line wrapping**.

## The wrapping problem

Since we (humanity) have been _writing_ text, we've been _wrapping_ it. Pages,
after all, have finite width. At some point, an ongoing sentence needs to
continue on the line below it. This is called _wrapping_. In digital text, there
are two kinds of wrapping: **soft** and **hard**. The former is much more
common, and we often take it for granted.

**Hard-wrapped text** is the simplest: the line breaks are directly part of the
source. If you're writing a sentence that's getting too long, you simply press
`<ret>` to begin a new line. The author is responsible for all line breaks. This
guarantees that, (assuming the renderer doesn't reflow text), the output will
always look _exactly_ how it does in the editor.

**Soft-wrapped text** has line breaks inserted by the _renderer_ --- they're
_not_ present in the source file. It's incredibly convenient! As the writer, we
don't need to worry at all about line breaks; only paragraph breaks. We can
trust that the text _will_ be wrapped properly whenever it's viewed.

Now... remember how I just said that, in the context of plain text email, we
can't make _any_ assumptions about how the text will be rendered? This applies
to wrapping, too. _Some_ mail clients may wrap text, **but not all of them**.
This essentially consigns us to hard-wrapping our emails.

The problem? _It's inconvenient!_ Imagine you edit a paragraph, and remove a
sentence. Well, now that entire paragraph's spacing is messed up, and you need
to manually reflow it and fix the line breaks. Yuck!

## The Markdown complication

### Standard tools

At this point, some of you may be screaming: _"but what about `fmt` and
`fold`?"_ There exist utilities meant to solve this specific problem, included
in most Linux distributions out-of-the-box! Well, you would be right. _Sort of_.

It's true that we already have excellent, composable commands for wrapping and
paragraph formatting. A simple `#!fish cat email.txt | fmt >email.txt` is enough
to cover many cases. However, there's a problem: **these tools are markup
agnostic**.

Why is that a problem when I literally [just](#plain-text-email) said we don't
care about markup? Well, there are _some_ markup formats that are delightfully
readable even in plain--text. Consider the following _unordered list_ in HTML
(Hyper Text **Markup** Format):

```html
<ul>
  <li>Foobar</li>
  <li>Barfoo</li>
</ul>
```

See, machines can read this no problem... but people? We struggle. Now, consider
the exact same expressed in [Markdown](https://en.wikipedia.org/wiki/Markdown):

```markdown
- Foobar
- Barfoo
```

Isn't that so much nicer? As it turns out, markup isn't only meant to make
writing HTML easier --- it's also a great way to enhance the _semantics_ of
plain text.

**This** is where we run up against issues with `fmt` & company: because they're
not _aware_ of Markdown syntax, they have a tendency to **break** it. Consider
the unordered list example from before:

```console
$ cat list.md | fmt
- Foobar - Barfoo
```

The tool has _no idea_ this is meant to be a list. It just treats whitespace
separated tokens as words and reflows paragraphs accordingly.

### Markdown formatters

My immediate next thought was to try an actual Markdown formatter. Not only do
they _also_ handle wrapping & reflow, they won't break the markup. I gave it a
shot, and to my horror, I found that they have the _opposite_ problem: they
preserve markup, but they break [signature blocks](#signature-blocks),
[sign-offs](#sign-offs), and [headers](#headers)!

## Writing `mailfmt`

I eventually wrote [`mailfmt`](https://git.ficd.sh/ficd/mailfmt) to fill the
niche of email formatting. It provides consistent paragraph spacing,
hard-wrapping and paragraph reflow, while preserving Markdown syntax, email
headers, quotes, sign-offs, and signature blocks. Additionally, the wrapped
output can be made safe for passing to a Markdown parser. This is useful if you
want to build an HTML email from plain-text.

`mailfmt` open-source under the ISC license, and is available on
[PyPI](https://pypi.org/project/mailfmt/) for installation with tools like
`pipx` and `uv`. The source code is available on sourcehut at
[git.ficd.sh/ficd/mailfmt](https://git.ficd.sh/ficd/mailfmt).

I wrote this tool primarily for myself. It's served me very well over the past
few months. `mailfmt` could be helpful for anyone that prefers writing email in
plain-text using text editors like Kakoune, Helix, and Vim. It can format via
`stdin`/`stdout` and read/write files, making `mailfmt` easy to configure as a
formatter for the `mail` filetype in your editor.

### My requirements

- A way to consistently format my outgoing emails in my text editor.
- Paragraph reflow and automatic line wrapping.
- Ability to use Markdown syntax:
  - Without it being broken by reflow & wrap.
  - While looking good and retaining the same semantics in _both_ rendered
    **and** plain-text form — ideal for `multipart` emails.
- _Ensure_ proper formatting of [signature blocks](#signature-blocks).
- _Preserve_ formatting of [sign-offs](#sign-offs).

### Wrap & reflow

It turns out that the most important part was also the easiest to implement.
Python's standard library includes
[`textwrap`](https://docs.python.org/3/library/textwrap.html), which _literally_
just does it for you. So the _real_ challenge becomes figuring out _what to
wrap_, versus **what to ignore**.

### Preserving Markdown

Getting my tool to preseve Markdown was fairly straightforward. I'm not building
a _Markdown formatter_, I'm building _a formatter that doesn't break Markdown_.
In other words, I don't need to _parse_ Markdown syntax; just recognize it,
**and ignore it**.

`mailfmt`'s approach is simple: detect when a line matches a known pattern of
Markdown block element syntax, such as leading `#` for headings, `-` for lists,
etc. If so, **leave the line untouched**. Similarly, **don't format anything
inside fenced code blocks**.

### Sign-offs

Consider the following sign-off:

```
Best wishes,
Daniel
```

A Markdown formatter considers this to be one paragraph, and reflows it
accordingly, causing it to lost semantic meaning:

```
Best wishes, Daniel
```

Within the confines of Markdown, I counted three ways of dealing with the
problem:

1. Put an empty line between the two parts:

```
Best wishes,

Daniel
```

> However, this empty line looks a tad awkward when viewed in plain--text.

2. Put a backslash after the intentional line break:

```
Best wishes, \
Daniel
```

> Again, this looks bad when the Markdown isn't rendered.

3. Put two spaces after the intentional line break (`•` = space):

```
Best•wishes,••
Daniel
```

> This syntax is **ambiguous, easy to forget**, and **not supported by editors
> that trim trailing whitespace.**

`mailfmt` detects sign-offs using a very simple heuristic. First, we check if a
line has _5 or less_ words, and **ends with a comma**. If we find such a line,
we check the _next_ line. If it has 5 or less words **that all begin with an
uppercase letter**, then we assume these two lines are a _sign-off_, and we
don't reflow or wrap them. The heuristic matches a very simple pattern:

```
A courteous salutation,
First Middle Last Name
```

### Signature blocks

The [standard](https://en.wikipedia.org/wiki/Signature_block#Standard_delimiter)
for signature blocks is as follows:

1. Begins with two `-` characters followed by a single space, then a newline.
2. Everything that follows until the EOF is part of the signature.

*[EOF]: End of file.

Here's an example (note the • = space):

```
--•
Daniel

Software•Developer,•Company
email@website.com
```

As with sign-offs, such a signature block gets mangled by other formatters.
Furthermore, the single space after the `--` token is important: if it's
missing, some clients won't recognize it is a valid signature.

`mailfmt` detects when a line's _only_ content is `--`. It adds the required
trailing space if it's missing, and it treats the rest of the file as part of
the signature, leaving it completely untouched.

## Headers

Raw emails contain many
[headers](https://en.wikipedia.org/wiki/Email#Message_header). Even if you're
reading/writing in plain--text, it's likely that your client strips these.
However, in some cases, you may want to insert a header or two manually.
Luckily, headers are easily matched by
[regex](https://en.wikipedia.org/wiki/Regular_expression), so `mailfmt` can
ignore them without any issues.

## Consistent multipart emails

Something you may want to do is generate a `text/multipart` email. This means
that _both_ an HTML **and** plain-text representation of the _same_ email are
included in the file — leaving it up to the reader's client to pick which one to
display.

The plain-text email **must** be able to stand on its own, and should _also_
render to decent-looking HTML. Essentially, you want to write your email in
plain-text once, ensuring it has proper formatting, and then use a command to
generate an HTML email from it.

For this, `mailfmt` provides the `--markdown-safe` flag, which appends
backslashes to the formatted output, making it safe for Markdown parsing without
messing up the line breaks after sign-offs and signature blocks.

Note that the **only** thing this does is output Markdown with hard line breaks.
It's the user's responsibility to write the pipeline for generating the email
file. For example, I use the following in [aerc](https://aerc-mail.org/) to
generate an HTML multipart email whenever I want:

```ini
[multipart-converters]
text/html=mailfmt --markdown-safe | pandoc -f markdown -t html --standalone
```

## Conclusion

If you've made it this far, thanks for sticking with me and reading to the end!
Even if you don't plan to write plain--text email or use `mailfmt` at all, I
hope you learned something interesting.