Re: [mailop] Outlook 2016: Excessive IMAP connections
Hi Tim No, ICMP is not being blocked. At least not on the IMAP server side. Yes, IPv6 in use, but the affected customer mostly don't use IPv6 and don't use mobile networks. But since we increased to 50 connections per user+ip the complaints are almost gone. As I understand, Outlook 2016 opens one connection per IMAP folder to get instantly notified (was this via IDLE command?) when something changes in the folder. So maybe a coincidence and many customers started exceeding the 20 folder limit? Mit freundlichen Grüssen -Benoît Panizzon- -- I m p r o W a r e A G-Leiter Commerce Kunden __ Zurlindenstrasse 29 Tel +41 61 826 93 00 CH-4133 PrattelnFax +41 61 826 93 01 Schweiz Web http://www.imp.ch __ ___ mailop mailing list mailop@mailop.org https://chilli.nosignal.org/cgi-bin/mailman/listinfo/mailop
Re: [mailop] Outlook 2016: Excessive IMAP connections
On 07/08/2020 19:31, Brandon Long via mailop wrote: Anyways, the point of my story is that it may not be a change to Outlook at all, but a Windows networking change or maybe just more network flakiness among your customers or even your own network (less likely). I wonder if the original poster by any chance has ICMP type 3 blocked in the firewall on the server end. I seem to be coming across more `connectivity` problems and sites that don't work with lower MTUs. Do you think that there is any chance the connection is managing the TLS and login with short packets, and then it hangs as soon as tries to move real data? Problems tend to appear if they have IPv6 and the customer's mobile network supports IPv6. Because blocking ICMP in IPv6 is just asking for trouble. Or the site doesn't have IPv6 and the customer's mobile network now uses 464xlat which _sometimes_ causes MTU issues, I think. There is more of this going on because the eyeball networks (particularly mobile) are out of nat capacity so trying to save costs and add capacity by adding IPv6. (which means IPv4 is inside the IPv6). (I'm big fan of IPv6. But when people decide they want to block ping, and so firewall all ICMP, they need sending back to networking school) -- Tim Bray Huddersfield, GB t...@kooky.org ___ mailop mailing list mailop@mailop.org https://chilli.nosignal.org/cgi-bin/mailman/listinfo/mailop
Re: [mailop] Outlook 2016: Excessive IMAP connections
>From my memory, Outlook would keep two connections open, one kind of "background / new mail" one, and one for the open folder. Our experience was that there were cases where flakey tcp paths could lead to long times for connections to die, though we were seeing it more with macbooks and apple mail than with Outlook. At one point we implemented a periodic untagged response to force a dead connection to die... but eventually we just moved to keeping track of the idle time on each connection and instead of blocking new connections, we would just kill the most idle one... though we would block a connection if there were no connections over a minimum idle threshold to prevent too many real connections from fighting for access. It's unfortunate that imap connections (at least ones that are in SELECTED state) are so heavy weight, otherwise we wouldn't need to care as much. Anyways, the point of my story is that it may not be a change to Outlook at all, but a Windows networking change or maybe just more network flakiness among your customers or even your own network (less likely). Brandon On Fri, Aug 7, 2020 at 8:34 AM Benoit Panizzon via mailop wrote: > Hi Gang > > We use DoveCot as IMAP Server and have limited the number of > connections per IMAP account to 20 which looks to have been sufficient > in the past couple of years. > > Since about two weeks we get an increased number of users complaining > about IMAP connections problem and name (0x8...) error message which > outlook 2016 throws at them. > > When looking at the log, we see those users sometimes hit the 20 IMAP > connections limit. So we increased this limit to 50 connections per > user+ip and they still hit it. > > This ONLY happens with customers using outlook 2016. Any other clients > never hit this issue. > > So I wonder if Microsoft has rolled out some weird update for outlook > 2016 lately or if anyone could have a hint on what causes this issue > and how to solve. > > Mit freundlichen Grüssen > > -Benoît Panizzon- > -- > I m p r o W a r e A G-Leiter Commerce Kunden > __ > > Zurlindenstrasse 29 Tel +41 61 826 93 00 > <+41%2061%20826%2093%2000> > CH-4133 PrattelnFax +41 61 826 93 01 > <+41%2061%20826%2093%2001> > Schweiz Web http://www.imp.ch > __ > > ___ > mailop mailing list > mailop@mailop.org > https://chilli.nosignal.org/cgi-bin/mailman/listinfo/mailop > ___ mailop mailing list mailop@mailop.org https://chilli.nosignal.org/cgi-bin/mailman/listinfo/mailop
[mailop] Outlook 2016: Excessive IMAP connections
Hi Gang We use DoveCot as IMAP Server and have limited the number of connections per IMAP account to 20 which looks to have been sufficient in the past couple of years. Since about two weeks we get an increased number of users complaining about IMAP connections problem and name (0x8...) error message which outlook 2016 throws at them. When looking at the log, we see those users sometimes hit the 20 IMAP connections limit. So we increased this limit to 50 connections per user+ip and they still hit it. This ONLY happens with customers using outlook 2016. Any other clients never hit this issue. So I wonder if Microsoft has rolled out some weird update for outlook 2016 lately or if anyone could have a hint on what causes this issue and how to solve. Mit freundlichen Grüssen -Benoît Panizzon- -- I m p r o W a r e A G-Leiter Commerce Kunden __ Zurlindenstrasse 29 Tel +41 61 826 93 00 CH-4133 PrattelnFax +41 61 826 93 01 Schweiz Web http://www.imp.ch __ ___ mailop mailing list mailop@mailop.org https://chilli.nosignal.org/cgi-bin/mailman/listinfo/mailop
