Präteritum and Perfekt
is the Präteritum preffered over the Perfekt in written german
I usually read Perfekt is for spoken, Präteritum is for written German. It can be a bit more detailed than that:
"Written German always uses the Präteritum more than spoken German, but just how much varies according to the context. The Präteritum is most favored in novels, history and other literary/academic writing."
But using Perfekt in e-mails is okay.
I confirm this, i am native speaker but its actually more extreme: there are some exceptions but NEVER use the Präteritum in common speech, the people would look at you xD The Perfekt is used in written language as well but only when its necessary in cases like: "The Minister has already give his permition". here youd also use the perfect in german, but in most cases the Präteritum or if necessary plusquamperfect (He had had)