This is how islam wants us to behave with people which are known or unknown to us.

Bismillah hir-Rahman nir-Rahim
Hadith: Khana khilao aur salam karo
Abdullah bin Amr Radi Allahu Anhu se rivayat hai ki Ek shaksh ne Rasoollallah Sallallahu Alaihi Wasallam se pucha islam mein kaunsi halat (ya baat) afzal hai Rasoollallah Sallallahu Alaihi Wasallam ne farmaya khana khilao aur salam karo usey jisey tum pahchantey ho usey bhi aur jisey tum nahi pahchantey ho usey bhi.
Sahih Bukhari, Vol 7, 6236
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Narrated 'Abdullah bin 'Amr Radi Allahu Anhu : A man asked the Prophet Sallallahu Alaihi Wasallam , "What Islamic traits are the best?" The Prophet Sallallahu Alaihi Wasallam said, "Feed the people, and greet those whom you know and those whom you do not know."
Sahih Bukhari, Vol 8, Book 74, No. 253