Used in the past to show deep respect, now it may sound out of place or overly formal.

Historical Politeness

You're not claiming to be an actual servant; it's just a respectful sign-off.

Not Literally

Best used in formal letters, especially when addressing someone of higher status or authority.

Indicates you're not serious and adds a humorous touch to your communication.

Can be used ironically in a situation where you have displayed independence or disagreement.

Can tease someone close, implying light-hearted subservience or mock deference.