要給namecheap的域名設置MX記錄，還略麻煩，直接設置不生效，于是乎看看文檔，發現：
NOTE:Before setting up your mail service, be sure that there is no CNAME record created for abare domain, (e.g.,yourdomain.tld) in theHost recordssection, or email will not work correctly. CNAME has the highest priority and prevails over all the other records for the host name, including MX Records which are responsible for mail delivery.
意思是說，設置郵件MX記錄之前，不能再host 記錄里面有頂級域名(一級域名)的CNAME記錄，否則不會MX生效，因為CNAME優先級別最高。
也就是說，先把CNAME刪除，在設置就OK了。設置成功后，在把CNAME加上即可。
