Learn Hardcore German: Es ist sinnvoll, eine eindeutige Adresse in der E‑Mail zu schreiben. - It is sensible to write an unambiguous address in the email.

Because the clause “eine eindeutige Adresse in der E‑Mail zu schreiben” is a zu‑infinitive group that is “announced” by the anticipatory pronoun es in the main clause (“Es ist sinnvoll, …”). In German, such infinitive groups are set off by a comma.

With anticipatory es: comma required.
If you front the infinitive group instead, there’s no comma: “Eine eindeutige Adresse in der E‑Mail zu schreiben ist sinnvoll.”

What does the “es” do here?

It’s a dummy or anticipatory subject. The real logical subject is the following infinitive clause (“eine eindeutige Adresse … zu schreiben”). German likes to keep the finite verb in second position, so es fills the subject slot: “Es ist sinnvoll, …” You can also put the infinitive clause first: “Eine eindeutige Adresse in der E‑Mail zu schreiben ist sinnvoll.”

Why do we need “zu schreiben” and not just “schreiben”?

German uses zu + infinitive to form infinitive clauses when they act like a noun phrase (subject/complement) after adjectives like sinnvoll, wichtig, leicht, etc. Without zu, the clause would be ungrammatical here. A common alternative is a dass‑clause with an explicit subject:

“Es ist sinnvoll, in der E‑Mail eine eindeutige Adresse zu schreiben.”
“Es ist sinnvoll, dass man/du in der E‑Mail eine eindeutige Adresse schreibst.”

Who is the implied subject of “zu schreiben”?

It’s generic/unspecified—roughly “one/you/people.” If you need to specify, switch to a dass‑clause: “Es ist sinnvoll, dass du … schreibst.”

Why is it “in der E‑Mail” (dative) and not “in die E‑Mail” (accusative)?

The preposition in can take dative (location) or accusative (direction/motion into). Here, “in der E‑Mail” is a location (where something is present), so dative is used. If you emphasize putting something into the email (direction), you can say “in die E‑Mail” with the accusative: “etwas in die E‑Mail schreiben.”

Which is more idiomatic here: “in der E‑Mail” or “in die E‑Mail”?

Both can work, but many speakers would phrase the advice as:

“Es ist sinnvoll, in der E‑Mail eine eindeutige Adresse anzugeben.” (talking about content present in the email) or
“Es ist sinnvoll, eine eindeutige Adresse in die E‑Mail zu schreiben.” (emphasizing the act of putting it in) In everyday advice about what an email should contain, “in der E‑Mail … angeben” is very natural.

Is “Adresse … schreiben” the best verb choice?

It’s understandable, but more idiomatic options for listing information in an email are:

angeben (to provide, to state): “in der E‑Mail eine eindeutige Adresse angeben”
nennen (to name)
eintragen/aufführen (to enter/list) “schreiben” is common in set phrases like “die Adresse auf den Umschlag schreiben,” but for email content, “angeben” sounds smoother.

Why “eine eindeutige Adresse” (those endings)? Why not “einen eindeutigen Adresse” or “ein eindeutige Adresse”?

Adresse is feminine: die Adresse.
It’s the direct object of “schreiben,” so accusative singular feminine.
After the indefinite article eine, the adjective takes the strong feminine accusative ending -e: eine eindeutige Adresse. “einen eindeutigen Adresse” is wrong (masculine endings on a feminine noun), and “ein eindeutige Adresse” is wrong (article doesn’t match feminine gender).

Does “in der E‑Mail” mean a specific email? Should it be “in einer E‑Mail” for a general statement?

“In der E‑Mail” can refer to a specific email already known in context. For a generic recommendation (“in an email”), in einer E‑Mail is often better:

“Es ist sinnvoll, in einer E‑Mail eine eindeutige Adresse anzugeben.”

What exactly does “eindeutig” mean here?

eindeutig = clear, unambiguous. It means the address leaves no room for misunderstanding. Don’t confuse it with einzigartig (“unique” in the sense of one-of-a-kind). In technical contexts, “eindeutig” can mean “unique (identifier),” but in everyday language it primarily means “unambiguous/clear.”

Is “E‑Mail” the correct spelling and gender?

Standard spelling: E‑Mail (capital E, hyphen). “Email” (no hyphen) is a different word in German meaning “enamel.”
Gender varies by region: in Germany, it’s usually feminine (die E‑Mail). In Austria (and parts of Switzerland), neuter (das E‑Mail) is common. This sentence uses the German-standard feminine: “in der E‑Mail.”

Why not “im E‑Mail”?

“im” = “in dem” (masculine/neuter dative). Since German-standard “E‑Mail” is feminine, you need in der E‑Mail, not “im.”

Is the word order inside the infinitive group okay? Could it be “in der E‑Mail eine eindeutige Adresse …”?

Yes. Both are possible:

“eine eindeutige Adresse in der E‑Mail zu schreiben”
“in der E‑Mail eine eindeutige Adresse zu schreiben” German tends to place known/short elements earlier and new/heavy elements later, so many speakers prefer “in der E‑Mail … eine eindeutige Adresse …” in this context. It’s a matter of flow, not strict rules.

Could I say “Es macht Sinn, …” instead of “Es ist sinnvoll, …”?

Yes, colloquially. Es macht Sinn is very common, though some style guides still prefer Es ergibt Sinn or Es ist sinnvoll in formal writing. All three are widely understood; “ist sinnvoll” is the safest in neutral/formal contexts.

Would “Es lohnt sich, …” work?

Yes, with a slightly different nuance:

Es ist sinnvoll, … = it’s advisable/wise.
Es lohnt sich, … = it’s worth the effort. Both are fine; pick the one that matches your intent.

Do I need to say “E‑Mail‑Adresse” if I mean an email address?

If you specifically mean an email address (like “name@example.com”), say E‑Mail‑Adresse:

“Es ist sinnvoll, in der E‑Mail eine eindeutige E‑Mail‑Adresse anzugeben.” “Adresse” alone can mean a postal address or other kinds of addresses, so adding “E‑Mail‑” removes ambiguity.