[Dovecot] Dovecot 2 and TCP-Keepalive

[Timo Sirainen]

On 20.10.2012, at 19.39, Sven Hartge wrote:

> I am about to migrate a perdition-based IMAP/POP3 proxy to Dovecot.
> 
> Unfortunately some users are behind a firewall/NAT setup which throws
> away seemingly idle TCP connections sooner than the established default
> of 24 hours (more likely after 30 minutes ...) resulting in all kinds of
> weird client behavior.
> 
> And unfortunately² this firewall/NAT setup is outside of my control and
> I have no means of correcting this (in my opinion) flawed configuration.
> 
> Now, with perdition I was able to use the --tcp_keepalive option which
> totally solved the mentioned weird client behavior.
> 
> My question is: does Dovecot2 use TCP-Keepalive on its sockets per
> default or do I need to enable it some way I have not yet discovered?

It's the default yes. Of course Linux's default keepalive interval is something like 90 minutes, so have you changed that already?..

> The manual and wiki only talk about "keepalive" in connection with the
> IMAP protocol and IDLE and my C-fu is too weak to understand the source
> code.

imap_idle_notify_interval (default 2 min) causes Dovecot to send data to IDLEing connections, which pretty much makes the TCP keepalive irrelevant. For non-IDLE connections Dovecot has a disconnect timeout of 30 minutes.