about send email

I have a barracuda which in china and a barruda in HK office.

I found that some domain (xxxx.com.cn) if send fr HK barrauda,it always delay over few hours.

But if xxxx.com.cn which send from my china barrada, it can go out normally

anyone have idea?

other side blocked? because if I change all email go fr china side, so many email which to USA/Hotmail/Yahoo...will be hold in barracuda over 1 days.....
So, we want use HK one to send the outgoing mail...but seem some China domain will be late too....
thanks