Same thing with “try to sound friendly.” Please and thank you are essential. But there are few things I hate more than cloying emails that start with “Hi!” (the exclamation point is the problem) and emoji are definitely worse.

Being polite is professional and shows mutual respect; IMO it implies an intention to build trust.

Affecting the trappings of friendliness or even loose intimacy in a professional setting or any setting where the relationship is in a rough spot has a strong chance of coming off as disingenuous.