Learn Swedish: Avsändaren har skickat avin till kunden. - The sender has sent the notification to the customer.

Yes! You can use the double object word order. To do this, drop till and place the indirect object (kunden) before the direct object (avin). The sentence becomes: Avsändaren har skickat kunden avin. Both versions mean exactly the same thing and are very common.

If I replace the nouns with pronouns (e.g., 'sent him it'), which word order should I use?

When both objects are pronouns, Swedish strongly prefers the double object order without a preposition. The indirect object (the receiver) still comes first. So, 'The sender has sent him it' would be: Avsändaren har skickat honom den. Using till here (skickat den till honom) is grammatically okay but can sound a bit clunky unless you are placing special emphasis on exactly who received it.

What is the base form of avin, and what exactly does it mean?

The base form is en avi. In Sweden, an avi (or postavi) is a specific paper slip or digital notification you receive telling you that a package is ready to be picked up at an agent. Since the base word ends in a vowel, it just takes an -n to become the definite form avin.

How is the word avsändaren built?