Очень моного отключений по Operation timed out

EEAA51872C1     9981 Tue Sep  8 17:22:40  o@f.ru
             (connect to mail.ntk.kis.ru[212.92.156.246]: Operation timed out)
                                         zykin@ntk.kis.ru

E3185187446    10001 Tue Sep  8 17:22:43  o@f.ru
             (connect to mail.ntk.kis.ru[212.92.156.246]: Operation timed out)
                                         alexandrov@ntk.kis.ru

E8C93187152    38205 Thu Sep 10 19:18:54  o@f.ru
          (connect to mail.elektronika.ru[83.229.248.15]: Operation timed out)
                                         minina.av@elektronika.ru

54F8A1871F1    38173 Thu Sep 10 19:12:47  o@f.ru
                    (connect to cezars.ru[193.232.159.1]: Operation timed out)
                                         Irinal@cezars.ru

56CA018710F    37993 Mon Sep  7 15:30:56  o@f.ru
                  (connect to 148.240.4.32[148.240.4.32]: Operation timed out)
                                         rakhimov@clear-vision.ru

7FFEE187075    37965 Mon Sep  7 15:23:23  o@f.ru
                  (connect to mail.arni.ru[212.118.35.2]: Operation timed out)
                                         marketing@arni.ru

724DA187187     9391 Tue Sep  8 17:11:40  o@f.ru
          (connect to mail.elektronika.ru[83.229.248.15]: Operation timed out)
                                         minina.av@elektronika.ru

7BC8118721A     9383 Tue Sep  8 17:07:39  o@f.ru
                  (connect to 148.240.4.32[148.240.4.32]: Operation timed out)
                                         loginov@stolichnoye.ru

972D1187197     9981 Tue Sep  8 17:16:59  o@f.ru
                   (connect to rcgroup.ru[194.85.89.197]: Operation timed out)
                                         oxana@rcgroup.ru

961D518750A    38197 Thu Sep 10 19:10:12  o@f.ru
                  (connect to 148.240.4.32[148.240.4.32]: Operation timed out)
                                         loginov@stolichnoye.ru

AD9E91874B8     9993 Tue Sep  8 17:15:43  o@f.ru
            (connect to gateway.opknn.ru[92.255.244.110]: Operation timed out)
                                         gleyberzon@opknn.ru

ACBD21871AA    38177 Thu Sep 10 19:04:12  o@f.ru
(delivery temporarily suspended: connect to mail.arni.ru[212.118.35.2]: Operation timed out)
                                         marketing@arni.ru

AB3371871A6    38177 Thu Sep 10 19:15:23  o@f.ru
                  (connect to mail.arni.ru[212.118.35.2]: Operation timed out)
                                         marketing@arni.ru

A36F71872EC     9997 Tue Sep  8 17:15:15  o@f.ru
       (connect to mail.begemot.nnov.ru[213.193.223.225]: Operation timed out)
                                         mail@begemot.nnov.ru

A9852187366     9973 Tue Sep  8 17:16:15  o@f.ru
                  (connect to 148.240.4.32[148.240.4.32]: Operation timed out)
                                         info@verley.ru

-- 1783 Kbytes in 76 Requests.
mail#

Делали, как когда-то предлагалось, изменить mtu на внешнем интерфейсе - не помогло, да и вебсерфинг останавливался.
Меняли количество smtp одновременных подключений в master.cf - не помогло.