Ef ég sendi bréfið í dag, ætti móttakandinn að fá það fyrir föstudag.

Senda is the infinitive, meaning to send. After ég, Icelandic needs a finite verb form, so you get ég sendi = I send.

A useful extra detail: in the 1st person singular, the present indicative and present subjunctive of many verbs can look the same, so sendi is simply the correct present form here.

Because ef introduces a subordinate clause, and subordinate clauses normally keep regular subject-verb order in Icelandic:

• Ef ég sendi... = If I send...

The inversion pattern that learners often notice in Icelandic mostly applies to main clauses, not to clauses introduced by ef.

This is because Icelandic is a verb-second (V2) language in main clauses.

The whole Ef ég sendi bréfið í dag counts as the first element. Once that first slot is taken, the finite verb of the main clause comes next, so you get:

• Ef ég sendi bréfið í dag, ætti móttakandinn...

If the sentence started directly with the subject, you would say:

• Móttakandinn ætti að fá það fyrir föstudag.

Ætti að fá means something like should receive, ought to receive, or would be expected to receive.

It comes from the construction eiga að + infinitive, which can express:

• obligation
• expectation
• what is supposed to happen

In this sentence, it is mainly about expectation: if the letter is sent today, the recipient can be expected to receive it by Friday.

Because ætti is a past subjunctive form that is often used with a modal meaning, not a literal past-time meaning.

So here it does not mean that the receiving happened in the past. Instead, it makes the statement a bit less absolute and more conditional or tentative:

• fær = receives / will receive
• ætti að fá = should receive / would be expected to receive

That is very common in Icelandic.

These two are easy to confuse, but they are different forms:

• átti = past indicative of eiga
• ætti = past subjunctive of eiga

Very roughly:

• átti að... often means was supposed to...
• ætti að... often means should... or would be expected to...

So in this sentence, ætti is the form that fits the conditional, expectation-based meaning.

The ending -inn is the suffixed definite article, so:

• móttakandi = recipient
• móttakandinn = the recipient

It is also in the nominative singular, because it is the subject of ætti að fá.

Yes, but it sounds somewhat more formal or written than everyday English the person getting it.

You will often see móttakandi in contexts like:

• letters
• parcels
• forms
• official language
• technical or administrative writing

So it is a perfectly normal word here, especially in a sentence about sending a letter.

Because bréf is a neuter noun, and -ið is the neuter singular definite article:

• bréf = letter
• bréfið = the letter

In this sentence, it is the direct object of sendi.

Það refers back to bréfið.

In Icelandic, pronouns agree with the noun’s gender and number. Since bréf is neuter singular, the matching pronoun is það:

• bréfið = the letter
• það = it

So að fá það means to receive it.

Because fá is an infinitive here, and the construction is ætti að fá.

With eiga að, Icelandic normally uses að + infinitive:

• ætti að fá = should receive

This is one of those places where Icelandic and English do not line up perfectly. English says should receive without to, but Icelandic uses að in this construction.

Because fyrir föstudag expresses a deadline:

• fyrir föstudag = by Friday / before Friday
• á föstudag = on Friday

So the sentence is not saying the recipient will get it on Friday specifically. It is saying Friday is the latest expected time.

Also, föstudag appears without an article because weekday names are often used that way in time expressions.