[root@postfix ~]# mailq
-Queue ID- --Size-- ----Arrival Time---- -Sender/Recipient-------
A5ACC2A23C4     1043 Wed Dec 30 15:38:57  from@yoursite.ru
(host mx.yandex.ru[213.180.193.89] said: 451 4.7.1 Sorry, the service is currently unavailable. Please come back later. 1451475538-V9prjhRGAZ-cwjGEwMT (in reply to end of DATA command))
                                         to-user@yandex.ru

0712B2A29C0     1035 Wed Dec 30 15:39:58  from@yoursite.ru
(host mx.yandex.ru[87.250.250.89] said: 451 4.7.1 Sorry, the service is currently unavailable. Please come back later. 1451475599-AHYpHhD6jV-dxoCCDhZ (in reply to end of DATA command))
                                         to-user@yandex.ru

-- 3 Kbytes in 2 Requests.

[root@postfix ~]#

9CB392A6D6D   672075 Tue May  8 14:10:58  from@yoursite.ru
(host ns.tgl.ru[194.67.32.36] said: 450 4.7.1 Client host rejected: cannot find your hostname, [80.80.80.80] (in reply to RCPT TO command))
                                         to-user@tgl.ru

F42042A3C6F     2322 Tue May  8 13:42:34  from@yoursite.ru
(delivery temporarily suspended: connect to usznco.ru[81.28.171.106]:25: Connection refused)
                                         to-user@usznco.ru

9FDB32A690D   672073 Tue May  8 14:05:04  from@yoursite.ru
                  (connect to ail.ru[91.195.240.135]:25: Connection timed out)
                                         to-user@ail.ru