Learn Dutch: Mag ik dat bericht nu sturen? - May I send that message now?

This is the verb bracket rule you are learning! When you use a modal verb like mag, it takes the main verb spot. The action verb (sturen) is then pushed to the very end of the sentence. Think of mag and sturen as two halves of a bracket holding the rest of the sentence together.

Why does the sentence start with Mag?

In Dutch yes/no questions, the verb and the subject swap places. The statement Ik mag (I may) becomes the question Mag ik? (May I?).

Why is it dat bericht and not die bericht?

The word bericht (message) is a het word (het bericht). When pointing to het words, you must use dat for 'that' and dit for 'this'. You only use die for de words.

Could I put nu at the very end, like in English ('...sturen nu')?

No, the infinitive verb (sturen) must be the absolute last word in this sentence because of the modal verb mag. Time words like nu (now) stay inside the sentence, safely before that final verb.