Im Betreff der E-Mail steht nur „Frage zum Kurs“.

Im Betreff means in the subject line.

• im = a contraction of in dem
• Betreff is a masculine noun, so dem is the correct dative article here

German often begins a sentence with a time/place/context phrase like this. Putting Im Betreff der E-Mail first sets the scene: we are talking about what appears in the email subject line.

Because im is the normal contraction of in dem.

So:

• in dem Betreff → im Betreff

Both are grammatically possible, but im is much more natural and common.

der E-Mail is in the genitive case and means of the email.

So:

• der Betreff der E-Mail = the subject line of the email

The noun E-Mail is feminine:

• nominative: die E-Mail
• genitive: der E-Mail

This is a very common German pattern: noun + genitive noun to show possession or close connection.

In German, stehen is often used for words or text that are written somewhere.

So Im Betreff der E-Mail steht nur ... literally means something like:

• In the email subject line, there stands only ...

That sounds odd in English, but it is completely normal in German.

You also see this with other written things:

• Auf dem Schild steht ... = The sign says ...
• In der Zeitung steht ... = The newspaper says ...

So steht is the natural verb here.

Because German main clauses follow the verb-second rule.

The first position is taken by:

• Im Betreff der E-Mail

So the finite verb must come next:

• steht

After that comes the rest:

• nur „Frage zum Kurs“

A more basic order would be:

• Nur „Frage zum Kurs“ steht im Betreff der E-Mail.

But the actual sentence sounds more natural because it starts with the context.

nur means only or just.

Here it tells you that the subject line contains nothing more than:

• Frage zum Kurs

So the sense is:

• The subject line only says “Question about the course.”

Its position before the quoted phrase shows that nur is modifying that phrase.

zum is a contraction of zu dem.

So:

• zum = zu dem

This is a very common contraction, like:

• am = an dem
• im = in dem

In Frage zum Kurs, the full form would be:

• Frage zu dem Kurs

But zum is the normal form.

German often uses Frage zu + dative for question about/concerning something.

So:

• eine Frage zum Kurs = a question about the course

English uses about, but German often prefers zu in this expression.

You may also hear Frage über ... in some contexts, but Frage zu is the standard, idiomatic choice here.

Because Kurs is masculine singular, and in this case the dative is shown by the article, not by a visible noun ending.

• der Kurs = nominative
• dem Kurs = dative

So in zum Kurs, the dative is already marked by dem inside zum.

Some masculine nouns do add an ending in certain cases, but Kurs does not here.

No. It is a noun phrase, not a full sentence.

It consists of:

• Frage = question
• zum Kurs = about the course

This is very typical for email subject lines, headlines, labels, and similar short written texts. German often leaves out articles in these contexts, just as English does.

Compare:

• Frage zum Kurs
• Problem mit der Anmeldung
• Terminänderung

These are not full sentences, but they work perfectly as subject lines.

Because subject lines often omit articles to stay short and compact.

So instead of:

• Eine Frage zum Kurs

the subject line just says:

• Frage zum Kurs

This is very natural in German. The same thing happens in English too:

• Question about the course
• not necessarily A question about the course

These are standard German quotation marks.

German usually writes quotations like this:

• „Text“

not like English:

• "Text"

So „Frage zum Kurs“ is just the German way of marking the exact text that appears in the subject line.

Because all nouns are capitalized in German.

So in this sentence, these are capitalized because they are nouns:

• Betreff
• E-Mail
• Frage
• Kurs

This is one of the most noticeable differences from English spelling.