I'd like my Gmail editor to enforce a maximum line width for emails I'm composing, say 70 or 80 chars. Is there a way to do this? Perhaps with a Chrome extension?
It doesn't look like there's any such tool out there.
Your most viable option is to use a text editor to compose your message and then paste it into a Gmail message. This might be helpful: How can I add line breaks to a text file?
If you are a Firefox user you can have line wrapping and many other editing and formatting features by simply using Thunderbird as your user client. You can have that and still use gmail as your email system. It will even provides utilities for backing up and restoring messages. Check out elegant user-designed free software at Mozzila.org. correte