本來今個月諗住忙d都launch左佢唔好再拖，好彩一時心血來潮試一試，一試之後就發現中左招，唔知點解唔work．
個case係佢收到email但係sent唔出，睇個/var/log/maillog就見佢係咁鬧” postfix/qmgr[4096]: warning: connect to transport smtp: Connection refused”，上google search都見到好多post，但係無一個可以solve到我個問題，我當然已經唔理三七二十一全部都跟住嚟做．
比佢玩左一日突然間腦部震盪，叮一聲記起我自己仲有另外一隻行梗無問題嘅MTA，於是就梗係馬上login睇下兩邊個config有d咩唔同啦．一睇之下就馬上發現原來我上次比人slide嘅時候亂咁改過d config去試吓係咩問題，當然試左一日都係無發現啦，後來咪知係比人slide左一獲勁架囉，唉！但係都係自己衰，唔記得backup起d config先玩，搞到衰左都唔知，唔知衰d咩果吓慘吖嗎．
Anyway，最後發現係/etc/postfix/master.cf入面有兩行smtp都比我remark左（無錯，係兩行）．unremark左之後梗係work返啦．得返之後又比我見到/var/log/maillog入面有d怪message"postfix/smtpd[8152]: connect from unknown[123.123.123.123]"，我份人就係咁，見到d唔想見或者係唔知係咩嘅嘢就好想整左佢，呢d唔知係唔係叫排除異己呢？
但係google左一輪都無發現，最後唯有放棄．之後就再browse http://jimsun.linxnet.com/misc/postfix-anti-UCE.txt去再harden個MTA多d，其實已經做左一定嘅UCE measure，但係還掂有時間，所以想再做多d，睇完哂之後就做左下面嘅measure．
smtpd_client_restrictions加左reject_unknown_reverse_client_hostname同埋reject_unknown_client_hostname
加呢兩個setting係想防止accept email from Unknown嘅host，包括無reverse PTR Record嘅server．但係點知加完之後，我用另外一部work緊嘅MTA send email去呢個新嘅MTA就點都唔得，/var/log/maillog就見”postfix/smtpd[8152]: NOQUEUE: reject: RCPT from unknown[123.123.123.123]: 450 4.7.1 Client host rejected: cannot find your hostname, [123.123.123.123]; from=<me@OKMTA.com> to=<me@newMTA.com> proto=SMTP helo=
諗來諗去都唔知點解，明明我部MTA果d DNS Record應該好齊吓架，有A, PTR同TXT(for SPF)嘅record，再者，我都無enable到SPF Checking．Google左好一陣，終於都比我搵到有人http://archives.neohapsis.com/archives/postfix/1999-q4/0199.html有d suggestion，佢話resolver唔一定搵bind，咁咪即係有機會要check吓/etc/nsswitch.conf．一睇之吓就發現"hosts: files dns"．哈哈，Resolvr果然係睇host，咁我咪試下改成"hosts: dns files”，改完咩都唔洗restart就得左．
雖然都知會對其他program有影響，好彩呢部係真係一部pure MTA所以應該無問題．而改完呢個setting仲搞掂埋"postfix/smtpd[8152]: connect from unknown[123.123.123.123]"添，其實果個post係唔關事架，但係睇吓睇吓又比我搵到d關聯．所以有時有問題不妨退一步，或者行開一吓，因為可能會比見到嘅所謂fact影響左，比佢帶完玩遊花園都未知架．
