Learn Swedish: Grannarna hämtar posten i varandras brevlådor. - The neighbors fetch the mail from each other's mailboxes.

In Swedish, whenever you use a possessive word—including the reciprocal genitive varandras (each other's)—the noun that belongs to it must be in the indefinite form. So it is varandras brevlådor, never varandras brevlådorna.

Why does the Swedish sentence use 'i' (in) instead of a word for 'from'?

In English, we usually say we fetch things from a container, but Swedish often focuses on where the object currently is located. You are fetching the mail that is in the mailbox (i brevlådan). You could use från (from), but i is a very natural and common choice here.

What exactly does 'hämtar' mean in everyday Swedish?

The verb att hämta means to go get something and bring it back. While it translates to 'fetch' here, it is the standard, everyday verb for picking up or collecting things. You use it whether you are getting the mail, picking up a package, or picking up your kids from school (hämta barnen).

What is the singular form of 'Grannarna'?

The singular is en granne (a neighbor). It is an en-word ending in -e, which means it forms its plural by dropping the -e and adding -ar to become grannar. To make it definite plural (the neighbors), you add -na, giving us grannarna.