dear instructor, sorry i havent finished the paper on time. lol.

Since I've received a number of ghastly abbreviation-filled, unpunctuated, lower-case, misspelled and generally unprofessional emails from my students lately, I am preparing to lead my class in a a discussion of email etiquette. I'm inviting suggestions. Tell me something one should never do (or always do) when writing a business- or school-related email to a colleague or superior.

Thank you!