EMOS無法接收郵件

今天有人說老總的郵箱無法接收126的郵件？大事啊。
於是登入後臺檢視，發現系統正常，而其他郵箱都正常接收郵件。最後檢查/var/log/maillog日誌檔案，發現以下資訊：

Mar 13 16:57:44 mail postfix/smtpd[24635]: disconnect from mail.abm-antriebe.de[62.153.229.221]
Mar 13 16:58:10 mail postfix/anvil[24580]: statistics: max connection rate 1/60s for (smtp:58.60.203.132) at Mar 13 16:48:10
Mar 13 16:58:10 mail postfix/anvil[24580]: statistics: max connection count 1 for (smtp:58.60.203.132) at Mar 13 16:48:10
Mar 13 16:58:10 mail postfix/anvil[24580]: statistics: max cache size 2 at Mar 13 16:50:43
Mar 13 16:59:51 mail postfix/smtpd[24670]: connect from unknown[113.89.127.165]
Mar 13 16:59:58 mail postfix/smtpd[24670]: lost connection after CONNECT from unknown[113.89.127.165]
Mar 13 16:59:58 mail postfix/smtpd[24670]: disconnect from unknown[113.89.127.165]
Mar 13 17:00:20 mail postfix/smtpd[24670]: connect from unknown[113.89.127.165]
Mar 13 17:00:39 mail postfix/smtpd[24676]: connect from mail.abm-antriebe.de[62.153.229.221]
Mar 13 17:01:05 mail postfix/smtpd[24676]: C420D1A04DD: client=mail.abm-antriebe.de[62.153.229.221]
Mar 13 17:01:06 mail postfix/cleanup[24689]: C420D1A04DD: message-id=<>
Mar 13 17:01:07 mail postfix/qmgr[14917]: C420D1A04DD: from=<>, size=18211, nrcpt=1 (queue active)
Mar 13 17:01:07 mail postfix/smtpd[24676]: disconnect from mail.abm-antriebe.de[62.153.229.221]
Mar 13 17:01:08 mail postfix/smtpd[24695]: connect from localhost.localdomain[127.0.0.1]
Mar 13 17:01:08 mail postfix/smtpd[24695]: 0D0F71A052C: client=localhost.localdomain[127.0.0.1]
Mar 13 17:01:08 mail postfix/cleanup[24689]: 0D0F71A052C: message-id=<>
Mar 13 17:01:08 mail postfix/qmgr[14917]: 0D0F71A052C: from=<>, size=19608, nrcpt=1 (queue active)
Mar 13 17:01:08 mail postfix/smtpd[24695]: disconnect from localhost.localdomain[127.0.0.1]
Mar 13 17:01:08 mail maildrop[24697]: Cannot have world/group permissions on the filter file - for your own good.
Mar 13 17:01:08 mail postfix/pipe[24696]: 0D0F71A052C: to=<>, relay=maildrop, delay=0.02, delays=0.01/0/0/0.01, dsn=4.3.0, status=deferred (temporary failure. Command output: maildrop: Cannot have world/group permissions on the filter file - for your own good. )
Mar 13 17:01:08 mail amavis[23969]: (23969-02) Passed CLEAN, [62.153.229.221] [62.153.229.221] <> -> <>, Message-ID: <>, mail_id: d3NY5AeI7RvV, Hits: -0.846, size: 18211, queued_as: 0D0F71A052C, 685 ms

最後確認發現.mailfilter檔案是在配置郵件過濾時產生的檔案，這個檔案的許可權必須是600，否則就會報錯：
Cannot have world/group permissions on the filter file - for your own good.
因為前幾天對兩臺伺服器做檔案同步，每晚自動複製主伺服器的檔案到備份伺服器，於是修改了所有的檔案許可權為755，所以導致該郵箱無法接收郵件。
發現問題後，把該檔案的許可權改回600，郵箱接收/傳送郵件恢復正常。

但是有個原因沒搞明白，為什麼許可權大了，反而不能接收郵件？