French phrase
Je vous serais reconnaissant de ~.
Meaning
I would be grateful if you could ___.
When to use it
A polite way to make a request. It is somewhat formal and indirect, often used with clients or superiors, and conveys appreciation in advance.
Example dialogue
Je vous serais reconnaissant de m'envoyer le rapport d'ici vendredi.
I would be grateful if you could send me the report by Friday.
Très bien, je vous l'enverrai demain.
Very well, I'll send it to you tomorrow.