How Sherlock survived and how Mr X got killed in his own game?

Question

One day James hired Mr X to kill Sherlock Holmes. Mr X disguised himself as an Insurance agent and called Sherlock Holmes for a meeting over a cup of tea. Mr X told the bartender to poison all the cups of Ice tea for their table. Somehow Sherlock Holmes get to know Mr X's plan to kill him. Still, he came to the meeting.

When Iced Tea came he immediately drunk 3 cups of Iced Tea while Mr X kept on looking at him drinking tea. Sherlock Holmes after finishing his tea pointed out that Mr X has not yet taken even one sip of his tea. Mr X saw Sherlock Holmes fully intact and thought that bartender forget to poison the tea. He slowly started drinking his tea and by the time he could finish half of his tea, he collapsed and dies of poison. Now all the cups of Iced Tea including the ones which Sherlock Holmes drunk were poisoned by the bartender.
Tell how Sherlock survived and how Mr X got killed in his own game?