On investigating some of our email-based replies that are below the default 20-character threshold, many of them are for short responses of affirmation, e.g. “sounds fine to me”, etc.
As I understand it, the character limit is designed to avoid just those type of responses in topics. One way to avoid user anger at the character limitation when they use email would be to include a link or button that would enable people to “like” the post for which they’re being notified.
That way, the user doesn’t have to struggle come up with some type of reply over 20 character minimum, and can voice their approval in 1 a single from their email client.