No enviïs el correu sense llegir la resposta.

Because Catalan uses the present subjunctive for negative commands.

So:

• Envia el correu. = Send the email.
• No enviïs el correu. = Don’t send the email.

For tu, the affirmative command is usually the imperative form (envia), but the negative command switches to the subjunctive (enviïs).

Enviïs is the 2nd person singular present subjunctive form of enviar (to send).

In this sentence, it is being used as a negative command addressed to tu:

• No enviïs = Don’t send

Related forms:

• No enviï = Don’t send (formal singular, vostè)
• No envieu = Don’t send (plural informal, vosaltres)
• No enviïn = Don’t send (formal plural, vostès)

The two dots are a diaeresis: ï.

In Catalan, this often shows that the i is pronounced separately, rather than blending into a diphthong. In enviïs, it helps signal the pronunciation of the verb form.

For a learner, the practical takeaway is:

• enviïs is a normal and expected spelling
• the ï is there for pronunciation/spelling reasons
• it is not optional

Because Catalan often drops subject pronouns when the verb already makes the subject clear.

So:

• No enviïs el correu...
  already clearly means Don’t you send the email... / Don’t send the email...

You could add tu for emphasis or contrast:

• Tu no enviïs el correu sense llegir la resposta.

That sounds more like You—don’t send the email without reading the reply.

Here el correu means the email / the mail, referring to a specific message or item.

Catalan uses the definite article in many places where English also uses the, so this is very natural:

• el correu = the email
• un correu = an email

Without the article, correu would usually sound less complete in this sentence.

It can mean either, depending on context.

• correu = mail / post / email
• correu electrònic = email, more explicitly

In modern everyday context, enviar un correu is very often understood as send an email. If you want to remove ambiguity, you can say correu electrònic.

Because sense + infinitive is the normal way to say without doing something when the subject is understood to be the same.

So:

• sense llegir la resposta = without reading the reply

This works like English without reading.

If you wanted a full clause with a different or explicit subject, Catalan often uses sense que + subjunctive instead.

For example:

• No enviïs el correu sense que ella llegeixi la resposta.
  = Don’t send the email without her reading the reply.

Because it refers to the reply/response, presumably a specific one already known from context.

Just like with el correu, Catalan uses the article naturally here:

• la resposta = the reply / the response
• una resposta = a reply / a response

So the sentence is talking about a particular response, not just any response.

Yes, but the given order is the most neutral and natural.

Standard order:

• No enviïs el correu sense llegir la resposta.

You could also say:

• Sense llegir la resposta, no enviïs el correu.

That puts more emphasis on without reading the reply.

Both are grammatical, but the original sentence is the most straightforward everyday version.

It attaches to the action of sending.

So the meaning is:

• Don’t send the email without reading the reply

It does not mean that the email itself is somehow without reading the reply. The phrase describes the condition under which the sending should or should not happen.

If you are speaking to vostè instead of tu, the verb changes:

• No enviï el correu sense llegir la resposta.

If you are speaking to vosaltres:

• No envieu el correu sense llegir la resposta.

So the rest of the sentence stays the same; the main change is the verb form used for the person you are addressing.