RFC 3676 specifies the email format options flowed. This format option allows for more dynamic and user-friendly line breaks. On, e.g. technical mailing lists, it is common to send Text/Plain emails and use something like 72 or 75 characters per line. The character limit can be traced back to the days when monitors were smaller and could only display 80 characters in each line. Nowadays, it is still common to comply with this limit in order to be backwards compatible, improve readability, and send patches on the mailing list without them being malformed.

The limitation of characters per line can lead to “embarrassing line wrap”. Furthermore, many people are used to having lines broken when they reach the border of their display window and not after 72 characters (also, on mobile devices, having hard line breaks can make it quite hard to read an email.)

When using format=flowed, a line is flowed when it ends in a space, if it ends in anything other than a space the line is fixed. A mail client that supports this format option can dynamically format the line length, while clients that don’t support this option can display the mail as if there would only be hard line breaks.

The following shows how I configured my mail client, in this case aerc and my editor Neovim which I use to read/write my emails. If you use a different mail client, the basic idea should be the same: Your mail client needs to add format=flowed to the email header, and the editor needs to format the text accordingly.

Configure aerc

I use aerc as my mail client, and setting format=flowed is relatively straightforward: In the aerc.conf set format-flowed=true in the [compose] section of the configuration.

Configure Neovim

To only use the formatting when writing emails, you need to figure out how the editor can identify that you are writing an email. When using aerc the filetyp is set to mail. Depending on your mail program, this might differ.

1. Create the directory after/ftplugin in your Neovim configuration. (e.g. .config/nvim/after/ftplugin/)
2. Create a Lua file with the same name as the filetype. (e.g. .config/nvim/after/ftplugin/mail.lua)
3. Insert into that file: vim.opt.formatoptions = "awq"

The options formatoptions awq mean (Neovim documentation):

a -> Automatic formatting of paragraphs.
w -> Trailing white space indicates a paragraph continues in the next line.
q -> Allow formatting of comments with “gq”.

This will allow you to have the correct formatting for format=flowed when only writing emails, and it won’t interfere with other document formats.