Privacy hazards (e.g. HTML is used to track users)
Some automated systems (e.g. mailing lists) do not accept HTML and
will reject messages, or use only the alternative plain text part, or
convert the HTML potentially causing formatting issues.
Requires HTML aware software
Double effort (HTML and text need to be formatted and
checked)
Little guarantee that HTML will be shown as intended
More distractions when writing (e.g. font selectors, emoji
buttons)
Harder to write (formatting takes more time)
“Angry fruit salad”: Every user chooses a
different font in a different color and different size.
Pro HTML mail
Ability to format and style the message content
Ability to create “rich” content (graphs, tables, …)
Ability to use semantic markup (e.g. to mark text as
preformatted)
Contra plain text mail
Text wrapping issues if lines are hard-wrapped (not format=flowed)
(e.g. on mobile devices with small screens)
Text formatted for fixed width fonts might get distorted
Some content is better sent as attachment (e.g. illustrations)
Pro plain text mail
Easy, small, ecologically friendly (compared to HTML mail)
Text is shown by all devices and programs
Accessibility as good as it gets
Criteria to consider
False positive spam: It is unclear whether HTML mails are more
likely to be falsely categorized as spam.
Accessibility: It is unclear whether HTML mails that include
alternative plain text parts are less accessible, for instance for text
to speech conversion.