Možností je mnoho : napr:
prej to máš zavírený, neskenuješ náhodou porty poštového serveru .... ? nekomunikuješ na porte kde to server neočakáva ? proste neco mu nepasuje ....SMTP Error 550 can also be returned by your own mail if thinks your email is spam
or dangerous for the recipient, other words it tries to protect your company from accidentally sending viruses and accidental spam emails – through a PC being infected