Spahn, Daniel wrote:
My setup is using the defaults, but the connection is so flaky that even pings
don't return consistently. My current setup no longer delivers mail, but I get
lots of timeout errors, and it looks like most messages end up in the defer
queue. Any ideas? This is a highly political situation and the people
responsible for fixing the problem will not work with me, yet I am responsible
for the proper functioning of this email system. Anything that even has a
slight chance of working will be greatly appreciated. To give a better picture
of the setup, I have a professional-grade multifunction device that scans,
faxes, prints, copies, etc.. It has a fixed IP on the LAN. Its scans go out to
the postfix server, which is connected to a Cisco switch, Netgear firewall, and
Cisco router/CSU/DSU. I have authentication turned on and it only accepts mail
from the multifunction device. It's not a high-traffic system- it just
occasionally has to send a few scans over email. I have administrat
ive access to the whole network, except the router/CSU/DSU (but any changes can
be requested if needed). Any advice that can mitigate the poor line quality is
appreciated.
You can tune postfix timeouts and retrys as described here:
http://www.postfix.org/TUNING_README.html#hammer
http://www.postfix.org/QSHAPE_README.html#queues
A very bad connection may drop before a message can get
delivered. If this happens often enough, it may make
communication impossible. SMTP requires that the connection
stays up long enough for the message to be transmitted.
(thinking out loud (often gets me in trouble)):
Sounds as if you are transmitting to a fixed destination. I
wonder if a UDP-based VPN (such as OpenVPN) might give you a
connection that drops less often. It wouldn't help with the
speed, but the drops are the big problem. Hmm, since most
VPNs support compression, maybe it could help with the speed.
You would need to have full control or significant cooperation
at the far end for a VPN to be possible.
You also may be able to tune some of your operating system TCP
parameters; increasing timeout and reducing max packet size
would seem to be a starting place. Check your OS docs for
how; google for tuning TCP for lossy connections.
I don't have much experience with a bad connection, so anyone
else feel free to jump in here...
--
Noel Jones
