Can you write "Hereby attached your reservation confirmation..." in an email?
I do not know if it is better to say: Hereby I send your reservation confirmation attached. Or something like that. Thank you for your help!
P.S. The reservation stuff is just an example. I am more concerned with how to express the "attached" part.

Question

Answer

I would use:
"I am attaching the confirmation for your reservation."
or
"I have attached the confirmation of your reservation"
or 
"Attached please find your reservation confirmation"  (if it's a very formal, very business context.)

I would not use "hereby."

Verpassen Sie nicht die Gelegenheit, bequem von zu Hause aus eine Sprache zu lernen. Stöbern Sie in unserer Auswahl an erfahrenen Sprachlehrern und melden Sie sich jetzt zu Ihrer ersten Unterrichtsstunde an!