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 name but with a lower-case letter if not.
Examples for the beginning of a letter
Including the commonly used blank line after the greeting, we could start a letter with
Sehr geehrte Frau Schmidt,
vielen Dank für ihren Brief.
In English, things are slightly different. The line directly after the greeting is considered to belong to a new sentence and therefore begins with a capital letter:
Dear Ms. Schmidt,
Thank you very much for your letter.
Examples for the ending of a letter
In German, you are not supposed to use a comma after the closing at the end of your letter/email and before your signature. The following example is therefore correct:
Mit freundlichen Grüßen
On the other hand, in English, the comma should not be dropped: