佞 character

佞 describes eloquence used to flatter or mislead.

The Chinese compounds 佞臣 (a minister who wins favor through flattery) and 佞言 (flattering or deceptive speech) show whether the criticism targets a person or their words.

what does 佞 mean when someone sends it?

Read it as a pointed literary insult.

By itself, it questions the target's character: polished words win favor at the expense of honesty. A quotation, classical text, or language lesson can make it descriptive rather than directed at the recipient.

If the sender seems to mean you, ask what passage or compound they have in mind before treating it as ordinary teasing.

why does 佞 have an older positive sense?

Its older range keeps verbal skill beside moral suspicion.

Shuowen Jiezi, an early Chinese dictionary, links the word with clever talent and flattery. A Japanese dictionary notes an early graph in a person's name on a bronze inscription (writing cast on a bronze object), and proposes that it depicts a capable woman serving a deity. That is a theory about the graph, not a settled origin.