Learn Hardcore German: Ich reagiere im Unterricht nicht sofort auf die E‑Mail. - I don’t respond to the email right away during class.

Yes, it’s Präsens (present tense): Ich reagiere …. In German, the present tense often also covers near-future meaning when the context makes it clear. For example, it can mean I don’t respond right away (when I’m in class), even though that describes a general/typical future situation.

What does im Unterricht mean exactly, and why is it im?

im Unterricht means in class / during class.
im is a contraction of in + dem:

in dem Unterricht → im Unterricht
Because Unterricht is masculine (der Unterricht), dem is the dative form used after in when it expresses location/time (not movement).

Why is nicht placed before sofort?

German places nicht close to what it negates. Here, the main idea being negated is sofort (immediately), not the whole action of reacting. So:

nicht sofort = not immediately
If you moved nicht, the focus could change. For example:
Ich reagiere im Unterricht sofort nicht auf die E-Mail. sounds unnatural and confusing.
Ich reagiere im Unterricht nicht auf die E-Mail. would mean I don’t respond to the email (at all) during class, not just not immediately.

Why does auf take die E‑Mail (accusative) here?

Because reagieren auf is a fixed verb + preposition combination, and auf in this meaning governs the accusative:

auf + Akkusativ → auf die E‑Mail
It’s not the “location” use of auf (which can switch between dative/accusative). With reagieren auf, it’s simply the required pattern.

Is die E‑Mail always feminine? Could I say das Email?

In standard German, E‑Mail is almost always feminine: die E‑Mail.
In some regions (especially Switzerland), you may encounter das E‑Mail or das Mail, but for most learners and most contexts, die E‑Mail is the safe default.

Why is the word order Ich reagiere … nicht sofort auf die E‑Mail and not … auf die E‑Mail nicht sofort?

German tends to place adverbials like nicht sofort before longer prepositional objects such as auf die E‑Mail. The version in the sentence sounds neutral and natural.
… auf die E‑Mail nicht sofort is possible, but it strongly emphasizes the email as the thing you’re (not) reacting to immediately, and it can sound marked or clunky without special context.

Could I use antworten instead of reagieren?

Often, yes, but the nuance changes:

antworten auf eine E‑Mail = to reply to an email (clear, direct)
reagieren auf eine E‑Mail = to react/respond to an email (slightly broader: could include reacting in other ways, not necessarily writing a reply)
If you mean specifically writing a reply, Ich antworte im Unterricht nicht sofort auf die E‑Mail. is very common.

Does im Unterricht refer to a school lesson only?

Not only. Unterricht can mean:

a school class/lesson
a university class
any teaching situation (e.g., music lessons)
If you mean “at work” or “in a meeting,” you’d normally use something else, like in einer Besprechung.

Why is Unterricht capitalized?

All German nouns are capitalized. Unterricht is a noun, so it must start with a capital letter.

What’s the difference between E‑Mail and Mail in German?

Both exist.

E‑Mail is the more explicit and standard term.
Mail is common in informal speech and writing, but it can sound slightly more casual or influenced by English.
The article usually stays die: die Mail / die E‑Mail.

Can I move im Unterricht to the beginning?

Yes, and German often does this to set the scene. The verb still stays in position 2 (V2 rule):

Im Unterricht reagiere ich nicht sofort auf die E‑Mail.
This emphasizes during class a bit more while keeping the meaning the same.