網管達人煩幫忙分析國外客戶常無法寄Mail至我方公司的問題

某大國外客戶Lx一直抱怨無法常會被退信(其它的國內外客戶無此問題),目前無解,弊公司
註冊網域時，申請2組IP.
這是國外客戶請IT分析的結果,IP我用XX來表示,可以幫忙分析是我方問題或是有其它問題點,因為對方是
國際級大客戶,mail server應也不會有問題才是....
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The cause of this problem maybe are two things.

(The problem as you know other all DNS(including my dns) get the wrong infomation for MX or A record of xxxxxxxx.com.tw

so can not send any mail to xxxxxxx.com.tw)

Frist, the DNS1.xxxxxxxx.com.tw has no "A" record on his two DNS(XXX.XX.XX.XXX, xxx.xx.xx.xx)
So Should change one dns name to DNS1.xxxxxxxx.com.tw like "DNS1.xxxxxxxx.com.tw internet address = xxx.xx.xx.xxx "
or "DNS1.xxxxxxxx.com.tw internet address = xxx.xx.xx.xx"
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> xxxxxxxx.com.tw
Server: 211-22-54-187.HINET-IP.hinet.net
Address: xxx.xx.xx.xx

xxxxxxx.com.tw nameserver = DNS1.xxxxxxxx.com.tw
xxxxxxx.com.tw nameserver = DNS.xxxxxxx.com.tw
DNS.xxxxxxx.com.tw internet address = xxx.xx.xx.xxx
DNS.xxxxxxx.com.tw internet address = xxx.xx.xx.xx

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Second, The two DNS (xxx.xx.xx.xxx, xxx.xx.xx.xx) should have the same "A" record for mail.xxxxxxxx.com.tw as followings

mail.xxxxxxxx.com.tw internet address = xxx.xx.xx.xx xxx.xx.xx.xx

Then Any other DNS ask ip for mail.xxxxxxxx.com.tw , he can get the two ip at same time,

Not like that now the other DNS get just one ip for mail.xxxxxxxx.com.tw wrongly.