Tanto la ortografía como el tono del correo tienen que ser correctos si no quieres dar una mala impresión.

In this sentence, tanto ... como ... means both ... and ....

So:

• Tanto la ortografía como el tono del correo = both the spelling and the tone of the email

This structure is very common in Spanish.

Examples:

• Tanto Ana como Luis vienen. = Both Ana and Luis are coming.
• Tanto el diseño como el contenido son importantes. = Both the design and the content are important.

Be careful: tanto can mean other things in other contexts, but here it is part of the fixed pattern tanto X como Y.

Because together they form a compound subject: two things joined by tanto ... como ....

• la ortografía = singular
• el tono = singular
• together = plural idea

So Spanish uses a plural verb:

• Tanto la ortografía como el tono del correo tienen que ser correctos.

This is just like English:

• The spelling and the tone have to be correct.

If there were only one subject, it would be singular:

• La ortografía tiene que ser correcta.

Because correctos agrees with both nouns together, and when Spanish has a mixed-gender plural group, it normally uses the masculine plural.

Here the two nouns are:

• la ortografía → feminine
• el tono → masculine

A mixed group becomes masculine plural:

• correctos

Compare:

• La ortografía es correcta. → feminine singular
• El tono es correcto. → masculine singular
• La ortografía y el tono son correctos. → masculine plural

So correctos is not referring only to tono. It covers both items.

Del is the contraction of de + el.

• de el correo → del correo

Spanish always contracts de + el into del.

So:

• el tono del correo = the tone of the email/message

But note:

• de + la does not contract
  
  • la ortografía de la carta
• de + los / las does not contract either
  
  • el tono de los correos

Also, there is no contraction with él meaning he:

• Hablo de él. = I’m talking about him.

In this sentence, correo most naturally means email, especially because the sentence talks about spelling and tone, which are very common concerns in written digital communication.

In Spain, people often say:

• correo
• correo electrónico
• sometimes email

So el tono del correo is naturally understood as the tone of the email/message.

If you wanted to be more explicit, you could say:

• el tono del correo electrónico

Because here it means if you don’t / if not, so it is:

• si = if
• no = not

So:

• si no quieres = if you don’t want

This is different from sino (one word), which usually means but rather / but instead, or appears after a negation.

Compare:

• Si no estudias, suspenderás. = If you don’t study, you’ll fail.
• No quiero té, sino café. = I don’t want tea, but rather coffee.

A quick test:

• If you can paraphrase it as if not, write si no
• If it contrasts one thing with another after a negative, write sino

Because the sentence is addressing you directly in the informal singular form (tú):

• si no quieres = if you don’t want

Forms:

• tú quieres = informal singular
• usted quiere = formal singular
• vosotros queréis = informal plural, very common in Spain
• ustedes quieren = formal/plural

So if you wanted a formal version, you could say:

• ... si no quiere dar una mala impresión.

And if speaking to more than one person in Spain:

• ... si no queréis dar una mala impresión.

Tener que + infinitive means to have to or must.

So:

• tienen que ser = have to be / must be

This is one of the most common ways to express obligation in Spanish.

Examples:

• Tengo que estudiar. = I have to study.
• Tenemos que salir. = We have to leave.
• El tono tiene que ser profesional. = The tone has to be professional.

In this sentence, it gives a fairly neutral, practical sense of obligation: these things need to be correct.

Yes, you could.

• tienen que ser correctos
• deben ser correctos

Both are natural and mean something like have to be / should be / must be correct, but the nuance can change slightly.

Very roughly:

• tener que often sounds more like a practical requirement
• deber can sometimes sound a bit more like advice, expectation, or moral duty

In this sentence, tienen que ser correctos sounds very natural and straightforward.

Because Spanish often uses definite articles more than English does.

Here, the sentence is talking about these two general but identifiable aspects of the email:

• the spelling
• the tone

So Spanish naturally says:

• la ortografía
• el tono

English might sometimes omit articles in similar contexts, but Spanish usually does not.

For example:

• La gramática es importante.
• El vocabulario también.

The articles help make the sentence sound complete and natural.

In this sentence, ortografía is best understood as spelling, but the Spanish word is slightly broader.

Ortografía can include:

• correct spelling
• correct written conventions
• sometimes punctuation and accent use, depending on context

So in everyday English translation here, spelling is the most natural choice, but the Spanish word can cover a bit more than that.

For example:

• Tiene buena ortografía. = He/She has good spelling.
• Hay errores de ortografía. = There are spelling mistakes.

Because dar una impresión is a standard Spanish expression meaning to give an impression / make an impression.

So:

• dar una mala impresión = to give a bad impression
• more naturally in English: to make a bad impression

Spanish often uses dar where English uses make.

Examples:

• dar una buena impresión = to make a good impression
• dar miedo = to cause fear / be scary
• dar vergüenza = to cause embarrassment

So this is not a word-for-word match with English, but it is the normal Spanish phrasing.

No, not here.

You need mala because it is an adjective modifying the feminine noun impresión:

• una mala impresión

Why?

• impresión is feminine
• singular feminine adjective form = mala

Mal is usually used differently:

• as an adverb: Está mal escrito. = It is badly written.
• before some masculine singular nouns: un mal día = a bad day

But with impresión, you need:

• una mala impresión

The sentence as given is very natural, but some parts can be changed.

Standard version:

• Tanto la ortografía como el tono del correo tienen que ser correctos si no quieres dar una mala impresión.

You could also say:

• Si no quieres dar una mala impresión, tanto la ortografía como el tono del correo tienen que ser correctos.

That simply moves the condition to the front.

What is less flexible is the core pattern:

• tanto X como Y

That structure should stay together.

Also, keeping correctos at the end sounds natural because it clearly applies to both la ortografía and el tono.

A slightly more formal version could be:

• Tanto la ortografía como el tono del correo electrónico deben ser correctos si no desea dar una mala impresión.

What changed?

• correo electrónico instead of just correo for extra clarity
• deben ser instead of tienen que ser for a slightly more formal tone
• desea instead of quieres because it uses usted

The original sentence is already completely correct and natural, though. It just sounds like it is speaking directly and informally to one person.