Learn Turkish: Göndericiye göre bu koli çok ağır. - According to the sender, this parcel is very heavy.

To say "according to" someone or something, you use the word göre. However, it always requires the word before it to be in the dative case (ending in -a or -e). That is why we say göndericiye göre instead of just gönderici göre.

Why does gönderici take the -ye ending instead of just -e?

The base word for sender is gönderici, which ends in a vowel. Because göre forces us to add the dative suffix -e, we have to insert the buffer letter -y- to stop the two vowels from crashing together.

How is the noun gönderici formed?

It is built from the verb root gönder- (send). By attaching the suffix -ici, which adapts to vowel harmony, we create a noun meaning "the one who does the action". Thus, gönderici means "sender".

Why isn't there a word for "is" at the end of the sentence?

In Turkish, present tense statements that describe a fact or state often leave "is" understood without any visible verb. The sentence literally reads "According to the sender this parcel very heavy". You could attach the "is" suffix -dir to the end to make ağırdır, but leaving it off is completely normal in everyday language.