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以前一直发送邮件很正常，最近出现发送邮件延迟好几个小时的情况，邮件日志如下，日志中可以看到"Could not retrieve PTR record for IP (false)! 223.xxx.xxx.140"，然后就加入了异步发送队列，所以延迟很久。
发送邮件的服务器上查询PTR都是有的，为啥还提示无法获取PTR记录呢，请高手指点

我的邮件服务器IP比如： 223.xxx.xxx.169，邮件域名：mail.xxxxxxx.com

PTR记录查询结果：
C:\Users\yb>nslookup -qt=ptr 223.xxx.xxx.xxx
服务器: UnKnown
Address: 172.16.56.11

非权威应答:
169.xxx.xxx.223.in-addr.arpa name = mail.xxxxxxx.com

3.xxx.223.in-addr.arpa nameserver = ns1.xgslb.net
3.xxx.223.in-addr.arpa nameserver = ns2.xgslb.net
3.xxx.223.in-addr.arpa nameserver = ns3.xgslb.net
3.xxx.223.in-addr.arpa nameserver = ns4.xgslb.net
ns1.xgslb.net internet address = 42.159.134.192
ns2.xgslb.net internet address = 42.159.8.176
ns3.xgslb.net internet address = 42.159.8.176


邮件日志：
"DEBUG" 1796 "2015-03-13 00:01:51.649" "Creating session 140768"
"TCPIP" 1796 "2015-03-13 00:01:51.649" "TCP - 223.xxx.xxx.140 connected to 10.124.153.251:25."
"DEBUG" 1796 "2015-03-13 00:01:51.651" "TCP connection started for session 140757"
"SMTPD" 1796 140757 "2015-03-13 00:01:51.651" "223.xxx.xxx.140" "SENT: 220 mail.xxx.com ESMTP"
"SMTPD" 4504 140757 "2015-03-13 00:01:51.652" "223.xxx.xxx.140" "RECEIVED: EHLO YB-WEB"
"SMTPD" 4504 140757 "2015-03-13 00:01:51.652" "223.xxx.xxx.140" "SENT: 250-mail.xxx.com[nl]250-SIZE 20480000[nl]250 AUTH LOGIN"
"SMTPD" 3472 140757 "2015-03-13 00:01:51.653" "223.xxx.xxx.140" "RECEIVED: AUTH LOGIN"
"SMTPD" 3472 140757 "2015-03-13 00:01:51.653" "223.xxx.xxx.140" "SENT: 334 VXNlcm5hbWU6"
"SMTPD" 4352 140757 "2015-03-13 00:01:51.654" "223.xxx.xxx.140" "RECEIVED: aW5mb0B5YW9mYW5nd2FuZy5jb20="
"SMTPD" 4352 140757 "2015-03-13 00:01:51.654" "223.xxx.xxx.140" "SENT: 334 UGFzc3dvcmQ6"
"SMTPD" 3472 140757 "2015-03-13 00:01:51.654" "223.xxx.xxx.140" "RECEIVED: ***"
"SMTPD" 3472 140757 "2015-03-13 00:01:51.657" "223.xxx.xxx.140" "SENT: 235 authenticated."
"SMTPD" 1796 140757 "2015-03-13 00:01:51.657" "223.xxx.xxx.140" "RECEIVED: MAIL FROM:<info@xxxxxx.com>"
"SMTPD" 1796 140757 "2015-03-13 00:01:51.658" "223.xxx.xxx.140" "SENT: 250 OK"
"SMTPD" 4504 140757 "2015-03-13 00:01:51.659" "223.xxx.xxx.140" "RECEIVED: RCPT TO:<xxxx@qq.com>"
"SMTPD" 4504 140757 "2015-03-13 00:01:51.661" "223.xxx.xxx.140" "SENT: 250 OK"
"SMTPD" 4352 140757 "2015-03-13 00:01:51.661" "223.xxx.xxx.140" "RECEIVED: DATA"
"SMTPD" 4352 140757 "2015-03-13 00:01:51.662" "223.xxx.xxx.140" "SENT: 354 OK, send."
"DEBUG" 4504 "2015-03-13 00:01:51.663" "Could not retrieve PTR record for IP (false)! 223.xxx.xxx.140"
"DEBUG" 4504 "2015-03-13 00:01:51.664" "Adding task AsynchronousTask to work queue Asynchronous task queue"
"DEBUG" 2368 "2015-03-13 00:01:51.664" "Executing task AsynchronousTask in work queue Asynchronous task queue"
"DEBUG" 2368 "2015-03-13 00:01:51.664" "Saving message: {1870D8C8-CF8A-4888-A856-77A850273E9B}.eml"
"DEBUG" 2368 "2015-03-13 00:01:51.667" "Requesting SMTPDeliveryManager to start message delivery"
"SMTPD" 2368 140757 "2015-03-13 00:01:51.667" "223.xxx.xxx.140" "SENT: 250 Queued (0.000 seconds)"
"SMTPD" 1796 140757 "2015-03-13 00:01:51.668" "223.xxx.xxx.140" "RECEIVED: QUIT"
"SMTPD" 1796 140757 "2015-03-13 00:01:51.668" "223.xxx.xxx.140" "SENT: 221 goodbye"
"DEBUG" 4352 "2015-03-13 00:01:51.668" "Ending session 140757"

诊断 有无问题？

诊断的话没有问题，PTR记录都有
PTR记录查询结果：
C:\Users\yb>nslookup -qt=ptr 223.xxx.xxx.xxx
服务器: UnKnown
Address: 172.16.56.11

非权威应答:
169.xxx.xxx.223.in-addr.arpa name = mail.xxxxxxx.com

3.xxx.223.in-addr.arpa nameserver = ns1.xgslb.net
3.xxx.223.in-addr.arpa nameserver = ns2.xgslb.net
3.xxx.223.in-addr.arpa nameserver = ns3.xgslb.net
3.xxx.223.in-addr.arpa nameserver = ns4.xgslb.net
ns1.xgslb.net internet address = 42.159.134.192
ns2.xgslb.net internet address = 42.159.8.176
ns3.xgslb.net internet address = 42.159.8.176

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