I'm not very familiar with English world, and I want to ask a question about Email etiquette.
Sometimes I sent an email to someone for help, and got a very helpful reply which completely solved my problem. When I was going to reply him, I found I have no more questions, so what I replied contains only two words 'Thank you'.
Do I really need to send this 'Thank you' letter? I think it's polite to show my gratitude, but it may also disturb him because this letter contains no real content.
Sorry for my bad English.