By default, Slack provides you with a Formatting toolbar and a WYSIWYG editor. I’m a big fan of writing in Markdown rather than WYSIWYG and use it everywhere I can. Fortunately, I can configure Slack to write in Markdown (or more accurately Slack’s subset of Markdown).
slack
Never write “thank you” in slack
While I would never suggest someone skip a “thank you”, I do recommend that you not type these words in slack.