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SmarterMail 12 connection limit
Problem reported by NOC - September 25, 2014 at 6:20 AM
Submitted
Hi,
 
Once I started with SmarterMail 12 I'm getting an issue with connection limit. This is mostly noticeable with IMAP. When user connections get around 400 IMAP start dropping new connections. It looks like this:
 
$  telnet mail.server 143
Trying 1xx.1xx.1xx.1xx...
Connected to mail.server
Escape character is '^]'.
Connection closed by foreign host.
 
It's no showing up even the banner. While trying the same two seconds later I get:
 
$  telnet mail.server 143
Trying 1xx.1xx.1xx.1xx...
Connected to mail.server
Escape character is '^]'.
* OK IMAP4rev1 SmarterMail
f logout
* BYE IMAP4rev1 Server logging out
f OK LOGOUT completed
Connection closed by foreign host.
 
 
I also run IMAPS on 993 and it works exactly the same way. It always start to happen when IMAP connections reach 380-410. I have set Max Connections for IMAP protocol to 0. Tried other bigger and smaller values. Nothing helps.
 
When it happens all other protocols are working just fine - SMTP, POP and HTTP are responding with no issue. Also I checked error log and no IMAP or connection related errors are logged.
 
With SmarterMail 11 I haven't experienced this.
 
The system is running on brand new and fully updated Windows Server 2012. What place I should look to get this solved? Anyone had the same issue? Any advice is much appreciated.
 
PP
 
 

4 Replies

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1
Tim Uzzanti Replied
September 25, 2014 at 8:31 AM
Employee Post
There is no change from 11 to 12 that would have any impact on connections.  SmarterMail doesn't really even manage the connections, we rely on the .NET Framework and Windows to do most of the work and notify us when there is a new connection and then we act on it.
 
SmarterMail itself has no set limits, we are only limited by the available hardware or performance of Windows.  When connections are being dropped, that is the OS making the decision and it often  related to issues from disk i/o, cpu, or some VM limit by the host etc.
 
If you want to provide a lot more info about your servers and configuration, we can give you some ideas.  But, there is a lot to evaluate and if your looking for quick results, it would be best to have our support team look at your server and evaluate the issue. We find crazy problems like Netowork Drivers or the need to disable CRC checks on a network card etc.  Our support often has to go FAR beyond SmarterMail and more into your Windows install.
 
Thanks,
 
Tim
Tim Uzzanti
CEO
SmarterTools Inc.
(877) 357-6278
www.smartertools.com
0
NOC Replied
September 26, 2014 at 12:48 AM
Hi Tim,
 
I just posted support ticket and will work from there.
 
The most irritating thing is it just started to happen after I switched to new server and new SmarterMail. I understand in this case we have million things to consider but it's just irritating that with enterprise class hardware, brand new operating system and latest version of SmarterMail software I get issues I never had on previous, crappy system.
 
It's bit strange to point on hardware because I should see the issue with all services not just IMAP.
 
Let's stop here. I'll update this thread once I get it solved within support ticket.
 
Thanks,
 
PP
2
Tim Uzzanti Replied
September 26, 2014 at 5:39 AM
Employee Post
I completely understand.  We will do out best to help you get to the bottom of it.
 
I have had my own experiences as well.  I had built one of the larger Windows hosting companies back in the day.  In the early stages we had finally made the decision that we were going to go with better hardware and build out an entire segment because we were growing so quick.  It was a big decision for us at the time.  So, we had purchased a bunch of hardware and found what we believed to be the perfect hardware configuration.  Then, we purchased enough hardware to build out a 100+ servers and built out the segment all at once.  We were sending shared sites in a round robin fashion to these 100 servers, so each server was slowly going from 1 to 2 to 3 sites etc.  After about 50 sites were on each of the servers they all started to fail.   We had tested this hardware configuration and it could have handled 400+ sites on each of the servers but after 50, everything was collapsing.  After many long sleepless nights, it came down to the RAID controllers.  Well, it turned out that the manufacturer had produced a bad batch of RAID controllers.  We had to hold things together for awhile until the manufacturer sent us new ones.  I wish this was the only story I had, but the list is endless.  There is so much that can go wrong hardware or software.  What is nice is that we have been there before and we try to help our customers through these things. Often, its not SmarterMail related but then sometimes it is.  In any case, I / We can sympathize with your situation :)
Tim Uzzanti
CEO
SmarterTools Inc.
(877) 357-6278
www.smartertools.com
0
NOC Replied
October 7, 2014 at 5:49 AM
Hi,
 
It's been more than 2 weeks without seeing this issue again. It stopped the same day I submitted support ticket to SmarterTools. You did the magic without touching anything :)
 
Seriously, the reason why it happened is still unknown. Right now I can just guess it was kind of DoS directed to IMAP. It's a bad guess because I would expect whole server going down in case of DoS.
 
It's not coming back now and I'm happy with this. Please consider this case closed.
 
Regards,
 
PP

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