小弟公司有2台 WebServer A(台灣)、B(大陸)，兩台用VPN相連
兩台都是用 CentOS + Nginx + PHP + MySQL
A server 有裝 Postfix 來寄 mail 且有使用帳密管制以防止垃圾跳板
B server 需要寄 mail 時，程式會登入到 A server ，再send出去。( 因為 B 在大陸，所以無法直接寄 Gmail )

A server send mail Hotmail、Gmail 都可以正常收到
B server send mail 則 Hotmail可以收到，Gmail會被擋

A server 寄 B server's mail 的 maillog , 其中比較令人在意是 message-id是空的 >.<?

Nov 11 17:30:19 ec1 postfix/smtpd[18550]: 11B0D360C68: **client=unknown[192.168.88.2], sasl_method=LOGIN, sasl_username=edm**
Nov 11 17:30:19 ec1 postfix/cleanup[18553]: 11B0D360C68: **message-id=<>**
Nov 11 17:30:19 ec1 postfix/qmgr[15737]: 11B0D360C68: from=<XXChina@XXX.com>, size=13314, nrcpt=1 (queue active)
Nov 11 17:30:19 ec1 postfix/smtp[18554]: connect to gmail-smtp-in.l.google.com[2404:6800:4008:c04::1b]:25: Network is unreachable
Nov 11 17:30:19 ec1 postfix/smtpd[18550]: disconnect from unknown[192.168.88.2]
Nov 11 17:30:20 ec1 postfix/smtp[18554]: 11B0D360C68: host gmail-smtp-in.l.google.com[74.125.203.26] said: 421-4.7.0 [60.249.152.90      15] Our system has detected that this message is 421-4.7.0 suspicious due to the very low reputation of the sending IP address. 421-4.7.0 To protect our users from spam, mail sent from your IP address has 421-4.7.0 been temporarily rate limited. Please visit 421 4.7.0  https://support.google.com/mail/answer/188131 for more information. dh16si2427802pac.207 - gsmtp (in reply to end of DATA command)
Nov 11 17:30:20 ec1 postfix/smtp[18554]: connect to alt1.gmail-smtp-in.l.google.com[2607:f8b0:4003:c03::1a]:25: Network is unreachable
Nov 11 17:30:22 ec1 postfix/smtp[18554]: 11B0D360C68: to=<funwinwu@gmail.com>, relay=alt1.gmail-smtp-in.l.google.com[74.125.30.27]:25, delay=3.6, delays=0.3/0.01/2.2/1.1, dsn=4.7.0, status=deferred (host alt1.gmail-smtp-in.l.google.com[74.125.30.27] said: 421-4.7.0 [61.218.229.39      15] Our system has detected that this message is 421-4.7.0 suspicious due to the very low reputation of the sending IP address. 421-4.7.0 To protect our users from spam, mail sent from your IP address has 421-4.7.0 been temporarily rate limited. Please visit 421 4.7.0  https://support.google.com/mail/answer/188131 for more information. i6si4997012oif.243 - gsmtp (in reply to end of DATA command))

想請問怎麼做，B server 的信件才不會被Gmail擋 ?