I have noticed that people with a German-speaking background often mix up conventions when writing letters and emails in English. For example, in German, the text directly after the greeting is considered to be a continuation of the greeting itself. Therefore, the first word starts with a capital letter if it is a noun or a name, and with a lower case letter else. Hence,
Sehr geehrte Frau Schmidt,
vielen Dank für ihren Brief.
However, in English, things are slightly different. The text following directly after the greeting is considered to be a new sentence, and hence begins with a capital letter:
Dear Ms. Schmidt,
Thank you very much for your letter.
Similarly, in German, you are not supposed to use a comma after the closing at the end of your letter/email and before your signature. Hence, while
Mit freundlichen Grüßen
is correct in German, the comma should not be dropped in