Trying to contact the Chinese embassy in Hanoi about applying for a visa.

I'm an American citizen trying to get in contact with the Chinese embassy in Hanoi, Vietnam regarding applying for a long-term Chinese visa, but when I send an email to the address listed on their main website, it keeps getting sent back to me with a failed delivery status. I am not too familiar with these sort of processes. Would I be able to enter the embassy during the 'working hours for consular department' as listed on their website, or do I have to call and make an appointment beforehand?