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Slow POP3 Server

Posted on 2000-02-29
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Last Modified: 2013-12-16
We have a pop3 server with a direct(DSL) connection to the internet. Our users are experiencing extreme latency in receiving their emails(sometimes overnight..sometimes more). The server is not behind a firewall, so that's not the problem. I've talked to our ISP and they say the DSL line is fine, except that our mail server "disappears" when there's no traffic on it. They suggested that I set up a continous ping to correct the problem. Has anyone had experience with this type of problem before? What's the best way to solve it?
What would be the best method for setting up a continous ping?
Thanks
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Question by:tibori
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jlevie earned 120 total points
ID: 2571093
They really said to ping the mailserver to fix it? Wierd...

Easy enough to do. Paste what's below into a file, make it executable, and fire it off when the system comes up.
/etc/rc.d/rc.local would be a good place to auto-start it.

#!/bin/sh
#
while true; do
ping -c 2 111.222.333.444 >/dev/null
sleep 60
done

I set it for two pings only every 60 seconds as that ought to be enough to keep everybody awake, adjust as you see fit.
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by:tibori
ID: 2571618
Well they said to ping their gateway machine from our mail server. They deny the problem is on their side, so I'm looking into our side. I'll try your suggestion tomorrow. Meanwhile can you think of any reason why a RH 5.2 machine(our mail server) would be "going to sleep" when there's no activity on it, and disappearing? To me it sounds like a problem on the ISP's side, but I don't know enough about Linux to make that conclusion.
Thanks
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by:jlevie
ID: 2573122
I've never encounter a system that exhibited that behaviour. I have seen driver/TCP stack problems that would cause a system to "pause" under very heavy network load, but that doesn't sound like it applies here.

While it wasn't your question, how about we examine the root problem a bit more closely. When you talk about latency do you mean the clients have problems connecting or that a message that should be in their inbox doesn't show up in a timely fashion.
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by:tibori
ID: 2573507
I mean the latter, that emails that were sent overnight, don't show up until the morning when all of them seem to come in at the same time. The clients are using MsWindows and Outlook, but the server is Linux based. I've checked for the clients having problems getting the mail from the server, but it's not the case. The emails actually don't arrive on the server either until early morning. The pattern to me seems to suggest that while the mail system is inactive during the night, it somehow is not recognized and the mail is held up somewhere. My colleague has tried to ping the mail server overnight, and he reported that it doesn't respond to the first few pings, and then it begins responding, just as if it had gone "offline" or something. Could it be something where the gateway machine for our ISP is losing the route to our machine due to inactivity??
Thanks for your help.
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by:tibori
ID: 2573560
Adjusted points to 30
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by:tibori
ID: 2573561
jlevie: I've set up the continous ping as you suggested. If it solves the problem, the points are yours. However I would still like to know your thoughts on a better solution.
Thanks
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by:jlevie
ID: 2573721
Disappearing routes would be my bet. The way to find out would be to not run the "pinger" overnight and have someone do a traceroute a couple of times and see where it gets stuck. If you want to give me the IP of the server I'd be willing to look at the routes. If you'd rather not expose the IP in a public forum you can send me the IP via email to jlevie@bellsouth.net. Also I'll need to know during what time period the "pinger" will be inactive (include timezone info please as I haven't a clue where you are)
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by:tibori
ID: 2576970
jlevie: We did the traceroute, and it stops on one of our ISP's machines. I've talked to them, and they say they'll look into it, but claim that they're not having similar problems with other clients, so it must be something that linux is doing. Where could I get more information on ipop3d and configuration parameters for it. I've already looked through the mail-user and the mail-administrator HOWTO's and I haven't found anything useful yet.
Thanks
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by:jlevie
ID: 2577140
Where did you do the traceroute from, the Internet? Since you know where it stopped, how many more hops from that point to your server?
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by:tibori
ID: 2577619
Yes, I traced from the internet. It would be either one or two hops from that point, not exactly sure. I'll try traceing it once when it's active. Any public places you know of that I could telnet to to play with this. I mean all of our machines are behind the firewall except for our mail server, so I don't have any 'outside' machine to ping the mailserver from, except from home when I connect to my ISP. Any ideas?
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by:jlevie
ID: 2577900
I don't know of any public telnet boxes, but if you'll send me the IP of your server (jlevie@bellsouth.net) or put it in a comment I'll trace it from here.
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by:jlevie
ID: 2581211
I traced the connect twice last night, but apparently there hadn't been a long enough period of inactivity to cause the timeout to occur.

I don't know how many users you have that would be inconvienced by one more night of delayed messages, but to really find out where it's breaking I've got see it when it's broken. We could arrainge to restart the pinger (from at) very early in the morning to minimize the imapct and I can give you a perl script that could be used to mail out a notice of the impending event, which would probably make it a bit more palatable.
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by:tibori
ID: 2581426
thanks jlevie for all your help. it seems(at least for the time being) that the problem has been solved. If it didn't time out last night, it may even be possible that our ISP had fixed their side of the problem, since I had contacted them on the issue. Either way, I don't mind having a ping on the system, as long as the problem's solved. If it occurs again, I'll let you know.
THANKS again
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