Is it obligatory to return the greeting every time the cafeteria worker passing by the employees repeats it, and is it permissible to prevent him from exaggeratedly repeating the greeting, given the Prophet's (peace be upon him and his family) saying that encourages spreading greetings?

Spreading peace (saying salam) is one of the hallmarks of Islam and a means of fostering love among Muslims. Initiating the greeting is a sunnah at every encounter, even if it is repetitive or from close proximity. Responding to the greeting is a fard kifayah (communal obligation). So, if one person is greeted, it becomes an individual obligation for them to respond. If a group is greeted, it suffices for one of them to respond. One should not be bothered by frequent greetings; rather, one should encourage those who frequently greet, as long as they adhere to the Shari'ah guidelines, such as not greeting someone who is preoccupied. If these guidelines are not observed, then one should advise against greeting the busy person. If they do not take heed, it is permissible to stop them.