Deafness

[Chris Ross]

> On Jul 28, 2015, at 21:52 , Steffan Cline <steffan at hldns.com> wrote:
> 
> Ok, I think I have come a little further.
> 
> When dovecot stops accepting connections, I checked netstat and found this:
> 
> [root at hosting1 ~]#  netstat -an | grep 993
> tcp        0      0 0.0.0.0:993                 0.0.0.0:*                   LISTEN      
> tcp        0      0 65.39.x.x:993            184.101.x.x:36351        SYN_RECV    
> tcp        0      0 65.39.x.x:993            107.212.x.x:51487        SYN_RECV    
> tcp        0      0 65.39.x.x:993            107.212.x.x:51488        SYN_RECV    
> tcp        0      0 65.39.x.x:993            184.101.x.x:44650        SYN_RECV    
> 
> This told me it wasn’t too many connections causing dovecot to be unresponsive. So then I tried via telnet.
> 
> Dovecot seems to accept connections but then just sits there and does nothing. I used the appropriate commands to try and initiate a login but nothing happens. Typing any commands at all produce no response from dovecot.

  Actually, I think the above shows that it’s not a dovecot problem.  A socket in a SYN_RECV state means that a connection request has been merely been received from the network.  That means your kernel has not finished establishing the TCP connection, so dovecot (or the application level in general) is likely not even involved yet.  I would suspect some sort of firewall config on your host, or perhaps some sort of overload at the network stack level.  But, the latter only if the server were very heavily loaded.

  I hope this feedback is helpful.

                                          - Chris