This email is in response to the complaint email received on date __/__/____ (date). I would like to offer my sincere apologies for not following company rules at office premises.
This is to inform you that I was not aware of the company rules and it was totally unintentional. I apologize for this unprofessional behavior and I regret the disturbance it may have caused to all the fellow employees. I assure you that I will follow the company rules and this incident will never happen again in future.
Please accept my apology and forgive me for the same. If you wish to contact me, you can always contact me at __________ (contact details).
___________ (Contact details)