A small correction to your sentences:
"Der Liefertermin wird in der Besprechung mit dem Kunden >am< Freitag, >dem xx.xx.2019< besprochen. Wir können Sie frühestens >am< Freitag, >evtl. auch erst Anfang nächster< Woche informieren."
As this is a business context, you should specify the exact date, because the expressions "diesen Freitag", "kommenden Freitag" and "nächsten Freitag" are not always understood in the same way by all Germans.
The word "Besprechung" is absolutely correct here, but "Mitteil" is not a word in German. Did you mean "Mitteilung" (message)? That would be something different. Or was it meant to be the English/Denglisch word "Meeting"? That one would also work, but I definitely prefer "Besprechung".