If I am thanking Amy, may I write:

"Thank you Amy" or "Thank you, Amy"?

Both seem correct, but this issue has given rise to a spirited debate

When directly addressing someone, the person’s name or title should be set off with commas:

Thank you for the lovely gift, Kim.

Thank you, Ed.

Thank you, Sir Edward, I'm much obliged.

That accords with the advice given in The Chicago Manual of Style, so you're on safe ground!



PaulM