I end all of my sentences with periods and I was told that I have a negative attitude at work because of it. Seriously, my manager's advice was to stop ending my sentences with periods.

There was a "right to be boring" lawsuit in France by an older employee who used vous instead of tu with his colleagues and subordinates, and was fired for it. He just wasn't comfortable in the informal register. If I recall correctly, he won.

You should consider finding other employment or at least another manager. If this is an example of how you are being evaluated in that organization, it can only get worse.

i sort of get it. or, at least, i can empathize with it.

my dad (in his 80s) ends 50%+ of his sentences in an ellipses. most people i know my age find it a bit jarring (is he mad? expecting more information?). and its not just him, ive met several people around the same age who have a similar habit in their writing.

so, when i had a similar conversation about coming across as rigid/negative with my emails, i figured it was a similar phenomenon between the younger generation and my generation as my generation and my dads. now i typically end with a "thanks!" to coworkers instead of "thanks.". not a big deal for me if it makes other people happier.

IIRC there was some psychological paper claiming that periods at the end of chat messages are bearing some emotional signal. I don't remember what it was exactly. I suppose your manager was too much into shitty psychological research.

In lieu of exclamation points? Or just run on chains of thought?