En el sótano hay tan poca cobertura que no puedo enviar el correo.

Because hay means there is / there are, so it is used to say that something exists or is present.

• Hay poca cobertura = There is little signal/coverage
• Está would be used to say where a specific thing is:
  • La cobertura está mal aquí = The signal is bad here

In this sentence, Spanish is expressing existence/availability of coverage in the basement, so hay is the natural choice.

Here, cobertura means signal coverage, especially mobile phone coverage or sometimes network coverage.

So tan poca cobertura means there is so little signal.

In Spain, this is a very natural way to talk about phone reception. You could also hear:

• No hay cobertura = There’s no signal
• Tengo poca cobertura = I have weak signal

Both are possible, but they do slightly different jobs.

• muy poca cobertura = very little coverage
• tan poca cobertura que... = so little coverage that...

The structure tan + adjective/adverb/quantity + que is used for a consequence:

• Hay tan poca cobertura que no puedo enviar el correo
  = There is so little signal that I can’t send the email

So tan ... que is a set pattern meaning so ... that.

Because cobertura is a feminine noun.

• la cobertura
• poca cobertura

The word poco/poca must agree with the noun:

• poca cobertura = little coverage
• poco tiempo = little time

So the ending changes because of grammatical gender.

Here que means that in the pattern so ... that.

The sentence is built like this:

• tan poca cobertura = so little coverage
• que no puedo enviar el correo = that I can’t send the email

So que introduces the result or consequence.

Because after poder, Spanish uses the infinitive directly.

• puedo enviar = I can send
• puedo hablar = I can speak
• puedo ir = I can go

There is no preposition between poder and the infinitive.

So:

• no puedo enviar el correo = I can’t send the email

It can mean either mail/post or email, depending on context.

In this sentence, because it talks about poor signal and sending something electronically, el correo most naturally means the email.

In Spain, people often shorten correo electrónico to simply correo when the meaning is obvious.

• Te mando un correo = I’ll send you an email

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

• enviar el correo electrónico

Because en means in, and Spanish normally uses it to show location.

• en el sótano = in the basement

This is made from:

• en
  • el = en el

Unlike a + el = al and de + el = del, en + el does not contract.

Because the stress falls on the first syllable: SÓ-ta-no.

Without the accent, Spanish spelling rules would suggest a different stress pattern. The written accent shows the correct pronunciation.

So it is:

• sótano

not:

• sotano

Yes, that is also correct, but it is structured differently.

• Hay tan poca cobertura que no puedo enviar el correo
  = There is so little signal that I can’t send the email
• No hay suficiente cobertura para enviar el correo
  = There isn’t enough signal to send the email

The first uses a so ... that structure.
The second uses enough ... to.

Both are natural. The original sentence sounds a bit more expressive.

Both are possible.

• enviar el correo
• mandar el correo

In Spain, both verbs are common, though enviar can sound a little more neutral or formal, and mandar can sound a bit more everyday depending on context.

For email, enviar is extremely common because it is also the standard verb used in apps and websites, like Send.

Because in Spanish, the present tense is exactly what you use for something happening now.

• no puedo = I can’t

It refers to the speaker’s current situation: right now, in the basement, they are unable to send the email.

Spanish does not need a special form like I am not able to here. The simple present is enough.

Yes, you could also say:

• Hay tan poca cobertura en el sótano que no puedo enviar el correo.

That is perfectly correct.

The original:

• En el sótano hay tan poca cobertura...

puts the location first, which gives a slight emphasis to in the basement.

So the difference is mostly about focus, not grammar.