German phrase
Ich schreibe wegen ~.
Meaning
I'm writing about ___
When to use it
It introduces your topic. It suits polite emails and careful explanations.
Example dialogue
Ich schreibe wegen eines Missverständnisses.
I'm writing about a misunderstanding.
Das tut mir leid, worum geht es genau?
I'm sorry, what exactly is it about?