你們 Email Server 出去的 IP 有設 Reversed DNS 反解嗎?

也就是: nslookup 得到的 IP, 與 nslookup 得到的 FQDN 必須是相同的, 對方才會讓你寄信 (如下圖兩者互查皆可獲得正確的資訊):

根據對方mail service provider 1&1 的訊息( http://d.pr/tENG/Hul0o4Jx)，你家mail server IP被列入黑名單了，他們使用的RBL是這個: http://dnsbl.info/ ，把你們家的mail server IP輸入進去檢查一下，如果被列入了請依照這個網站上的指示做移除動作。

554 No SMTP service - IP address is black listed
In order to reduce the number of spam e-mails received in our system, we use common RBL-lists to reduce the receipt of e-mail spam. These lists include dynamic IP addresses and IPs contain IP addresses which are dynamic on the one hand side and associated with sending known to send spam messages on the other hand. DNSBL.info may be used to verify if an IP address is on one of the above mentioned lists.