Greeting with a smile is good deed and Sunnah

A Happy And Smiling Face

Ibn Battaal said:

‏«انَّ لقاء النَّاس بالتَّبسُّم وطلاقة الوجه من ‏أخلاق النُّبوة وهو مناف للتكبُّر، وجالب للمودَّة»

❝Verily, greeting people with a smile and a happy face is from the prophetic manners, it removes arrogance, and attracts love.❞

[From Explanation of Saheeh Bukhari, (5/193) | Translated By Abbas Abu Yahya Miraath al-Anbiyya]