Learn Hardcore German: Diese Vorlage ist praktisch; mit der Vorlage schreiben wir die E‑Mails schneller. - This template is practical; with the template we write the emails faster.

Because the preposition mit always takes the dative case. The noun Vorlage (template) is feminine, and the dative singular article for feminine nouns is der.

Nominative: die Vorlage
Accusative: die Vorlage
Dative: der Vorlage So: mit der Vorlage = with the template.

Could I say "mit dieser Vorlage" or use a pronoun like "damit" instead of repeating "Vorlage"?

Yes.

mit dieser Vorlage keeps the demonstrative and is perfectly fine.
damit is a very idiomatic “prepositional adverb” meaning “with that/it”: Diese Vorlage ist praktisch; damit schreiben wir die E‑Mails schneller.
You can also say mit ihr (with her/it), because Vorlage is feminine: Mit ihr schreiben wir .... However, damit is often the clearest choice.

Why does the verb come before "wir" in "mit der Vorlage schreiben wir"?

German is a verb-second (V2) language in main clauses. If you put something other than the subject first (here, the prepositional phrase mit der Vorlage), the finite verb must still be in second position, so the subject wir comes after the verb:

Neutral order: Wir schreiben mit der Vorlage die E‑Mails schneller.
Fronted phrase for emphasis: Mit der Vorlage schreiben wir die E‑Mails schneller.

Could I just use a comma instead of the semicolon?

Not by itself. In German, a comma cannot simply join two independent main clauses unless you also add a coordinating conjunction (e.g., und, aber, denn). Options:

Keep the semicolon: Diese Vorlage ist praktisch; ...
Make two sentences: Diese Vorlage ist praktisch. Mit der Vorlage ...
Use a conjunction: Diese Vorlage ist praktisch, denn mit der Vorlage schreiben wir ...
A colon can also work for explanation: Diese Vorlage ist praktisch: Mit der Vorlage ...

Why is "mit" lowercased after the semicolon?

After a semicolon in German, the next word is normally lowercase (unless it needs capitalization for other reasons, e.g., it’s a noun or a proper name). So ... ist praktisch; mit der Vorlage ... is correct.

Why is it "praktisch" and not "praktische"?

After the verb sein (to be), adjectives are used in their base, uninflected form (predicative use): Die Vorlage ist praktisch. Adjectives only take endings before a noun (attributive use): eine praktische Vorlage.

Why "schneller" and not "mehr schnell"?

German generally forms the comparative by adding ‑er to the adjective/adverb: schnell → schneller. You don’t say mehr schnell. A few words are irregular (gern → lieber, viel → mehr), but most follow the ‑er pattern.

Where should "schneller" go in the sentence? Could I say "Wir schreiben schneller die E‑Mails"?

The natural place is toward the end: Wir schreiben die E‑Mails schneller.
You can front it for emphasis (Schneller schreiben wir die E‑Mails), but Wir schreiben schneller die E‑Mails is unusual and usually avoided. Don’t say schnellere E‑Mails here—that would mean the emails themselves are “faster,” not the act of writing them.

Can I drop the article and say "Wir schreiben E‑Mails schneller"?

Yes. Without the article, it’s a general statement about emails in general. Using die E‑Mails points to specific emails already known in context. Both are grammatically correct; choose based on meaning.

Is "E‑Mail" spelled with a hyphen? Is "Email" okay?

The standard spelling is E‑Mail (with a hyphen). The plural is E‑Mails. Writing Email (without a hyphen) is a different German word meaning “enamel.” Colloquially, many people also say Mail(s), which is acceptable in informal contexts.

Why is the M in E‑Mail capitalized?

In hyphenated German compounds, each part retains its original capitalization. Mail is a noun, so it’s capitalized: E‑Mail. (You’ll see stylistic variants like “E-mail,” but E‑Mail is the Duden standard.)

Could I use "weil" or "denn" instead of the semicolon to express the reason?

Yes.

denn (coordinating): Diese Vorlage ist praktisch, denn damit schreiben wir die E‑Mails schneller. (Main clause word order stays V2.)
weil (subordinating): Diese Vorlage ist praktisch, weil wir die E‑Mails damit schneller schreiben. (Verb goes to the end in the weil‑clause.) You can also keep mit der Vorlage inside the clause: ..., weil wir mit der Vorlage die E‑Mails schneller schreiben.

Can I turn the second clause into a relative clause?

Yes: Diese Vorlage, mit der wir die E‑Mails schneller schreiben, ist praktisch.
Here mit der uses the relative pronoun in the dative feminine (agreeing with Vorlage). You’ll also see womit in some styles, but mit der is the clearest when the antecedent is explicitly named.

Why not use "durch die Vorlage" instead of "mit der Vorlage"?

mit expresses the instrument/tool you use. durch focuses on causation or passage (“through/by means of”) and would sound odd here. More formal synonyms for “using” include mithilfe der Vorlage or mittels der Vorlage.

Isn’t "der" masculine? How can "der Vorlage" be feminine?

The article der is used for multiple things in German. It’s masculine nominative singular (der Mann), but it’s also the dative feminine singular (der Frau) and the genitive feminine singular (der Frau). Here it’s dative feminine because of mit: mit der Vorlage.

Could I use "man" instead of "wir"?

Yes. Mit der Vorlage schreibt man E‑Mails schneller. Using man makes the statement general (“one/people in general”).

Is "schreiben" the best verb here, or could I say "verfassen" or "tippen"?

All work, with nuances:

schreiben: the default, neutral “to write.”
verfassen: a bit more formal/literary, “to compose.”
tippen: emphasizes typing on a keyboard.
Example: Mit der Vorlage verfassen/tippen wir die E‑Mails schneller.