Sometimes I read some emails, people will reply "Noted" or "Noted with thanks", that means they understood or they got it, I'd like to know if it is a proper English in email? Please advise. Thanks
The phrase 'Noted with thanks' is fine in any informal context; it's not informal, but the grammar is. Formally, you would need a bit of grammatical padding - along the lines of 'Your very fiull comments are noted with thanks'.