French phrase
Je vous répondrai d'ici ~.
Meaning
I will reply to you by ___.
When to use it
A clear promise to reply by a stated deadline. It works in both written and spoken communication.
Example dialogue
Je vous répondrai d'ici la fin de la semaine.
I will reply to you by the end of the week.
C'est noté, merci.
Noted, thank you.