POP connection problem

[tsimtung]

Hi, some users said that sometimes they have connection problem,s I check the log:
Jul 20 22:03:05 aliyun23 dovecot[101155]: pop3([email protected])<163403><Z4Vxm+sAcMxxWqca>: Disconnected: Connection closed: Connection reset by peer top=3/15305, retr=1/0, del=0/2972, size=2459988205, bytes=56/1960311
Jul 20 22:13:06 aliyun23 dovecot[101155]: pop3([email protected])<164371><944+v+sA+cpxWqca>: Disconnected: Connection closed: Connection reset by peer top=3/15305, retr=1/0, del=0/2972, size=2459988205, bytes=56/1927239
Jul 20 22:23:08 aliyun23 dovecot[101155]: pop3([email protected])<165393><U9ol4+sAOsFxWqca>: Disconnected: Connection closed: Connection reset by peer top=3/15305, retr=1/0, del=0/2972, size=2459988205, bytes=56/2022321
Jul 20 22:33:09 aliyun23 dovecot[101155]: pop3([email protected])<166692><4GjxBuwAuMpxWqca>: Disconnected: Connection closed: Connection reset by peer top=3/15305, retr=1/0, del=0/2972, size=2459988205, bytes=56/1894167
Jul 20 22:43:10 aliyun23 dovecot[101155]: pop3([email protected])<167896><gWbAKuwAccNxWqca>: Disconnected: Connection closed: Connection reset by peer top=3/15305, retr=1/0, del=0/2972, size=2459988205, bytes=56/1960311
Jul 20 22:53:10 aliyun23 dovecot[101155]: pop3([email protected])<168977><CkqMTuwAvMVxWqca>: Disconnected: Connection closed: Connection reset by peer top=3/15305, retr=1/0, del=0/2972, size=2459988205, bytes=56/1894167
Jul 20 23:03:11 aliyun23 dovecot[101155]: pop3([email protected])<170060><GMpccuwA/cVxWqca>: Disconnected: Connection closed: Connection reset by peer top=3/15305, retr=1/0, del=0/2972, size=2459988205, bytes=56/1989249
Jul 20 23:03:11 aliyun23 dovecot[101155]: pop3([email protected])<170062><FQ1ncuwA/sVxWqca>: Disconnected: Connection closed: read(size=2048) failed: Connection reset by peer top=0/0, retr=0/0, del=0/2972, size=2459988205, bytes=0/16
Jul 20 23:13:12 aliyun23 dovecot[101155]: pop3([email protected])<171014><Yd8rluwAzMFxWqca>: Disconnected: Connection closed: Connection reset by peer top=3/15305, retr=1/0, del=0/2972, size=2459988205, bytes=56/2055393


What is this problem? how to solve it?