formal emails have at least 4 newline characters, thus less newlines could identify start-chat email messages, together with a reduced max. character limit of say 250. This “email text” post, for example, has 344 characters, should it prompt a “Start chat?” question, by default, if the “cheers and name” are on a single line instead?
I would say above message is too long for considering it a chat candidate, by default, even if the greeting at the end would only be written on one single line, and thus the message would only have a total of 3 newlines (manual carriage returns).
So it seems to me a maximal length of 250 characters for determining start-a-chat emails may work more cleanly, with less false positives. (Remember that follow up chat-answers may be longer.) It’s just the start-chat threshold. The new email counter icon will still be able to provide the status for any longer emails.