Breakdown of Я должен отправить отчёт до перерыва.
я
I
отправить
to send (perfective)
должен
must, have to (должен, должна, должны)
отчёт
report
Questions & Answers about Я должен отправить отчёт до перерыва.
Why does the word for break change to перерыва in this sentence?
The word перерыв is following the preposition до (before or until). This preposition always requires the genitive case. Since перерыв is a masculine noun ending in a consonant, we add -а to make it перерыва.
Is должен a verb, and does it change depending on who is speaking?
должен (must or have to) is actually a short-form adjective, so it changes based on the gender of the subject. Since it is должен here, we know a man is speaking. A woman would say Я должна, and a group would say Мы должны.
отчёт (the report) is the direct object being sent. Why doesn't its ending change?
It is in the accusative case, but for masculine inanimate nouns (objects, not people or animals), the accusative form looks exactly the same as the nominative dictionary form. So отчёт does not change its ending.
Why use the perfective verb отправить instead of the imperfective отправлять?
The speaker needs to complete a single, specific action (sending this one report) and achieve a result before the deadline. We use perfective verbs for one-time, completed actions like this.