I can’t say anything useful about short-form email (I have never been comfortable with it, to be honest), but in IM the termination requirement feels to be already satisfied by the built-in separation between messages—in longer messages, I frequently end up using periods as statement separators rather than terminators. The only reason to use a final period, then, becomes to attach a feeling of additional abruptness or finality to the last sentence, which easily reads as (passive-)aggressive or dismissive. (I’m not saying “offensive” as that’s really more about the perception of the recipient, but these two are about the intent of the originator.)
The conventions for formal messaging and informal messaging are different, and punctuation is a contextual marker for formality. Receiving a reply to a physical letter that read, on company letterhead and with a physical signature
Taxcoder, regarding your proposed changes,
Ok.
Sincerely, Jim Bossman
would be a bit alarming, because it's clear that the letter is a very formal one, but it deliberately omits everything you'd normally put in a letter. If you instead found your proposal mailed back to you with
OK - Jim Bossman
written on the bottom in red pen, you wouldn't be at all worried, although depending on the context you might be insulted by the informality.
I think if a message without punctuation seems sloppy, the situation is formal enough to write a full sentence or paragraph. The combination of little to no feedback and attention to detail is what worries people.
"Ok" is ever more informal than "Ok." The decision whether or not to add the period is of course not always a matter of trying to sound more assertive, but in a three character message that potential cue will necessarily be "scaled up".
Thanks for the response. As SquareWheel also commented, the lack of punctuation seems disinterested or dismissive to me. I suppose my criticism of lack of punctuation is not different than others criticism of its inclusion.
I read it completely differently. I see a sentence without punctuation as disinterested, as if they don't even bother to complete the sentence. Maybe acceptable in an IM, but not an email.
I tend to stay away from one word replies, and if I need to confirm use 10-4 or wilco. Are either of those offensive?