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Number of connections per IP / POP3
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Zeitkind Offline
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Post: #1
Number of connections per IP / POP3
FYI:
There is an issue with Mac OS X 10.6-users with Apple Mail. Apple decided to thread all outgoing pop3-connections, so if you have 10 pop-accounts on the same server, you open 10 connections.. and randomly the accounts go offline in the Mail program.
In ispcp the default for courier is 4 connections, so it would be nice to alter the setting in the GUI, otherwise you need to change it in /etc/courier/pop3d.
Not much of an issue, but if someone has this problem..
02-25-2010 03:49 AM
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BeNe Offline
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Post: #2
RE: Number of connections per IP / POP3
We use all defaults from the Courier-Package so it is not really ispCP related.
In my eyes this is the work of the Sysadmin and not the work for the ispCP gui or ?

Maybe Dovecot works here better ?!

Greez BeNe
02-25-2010 05:14 PM
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rbtux Offline
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Post: #3
RE: Number of connections per IP / POP3
well I don't get why one would use pop3 these days... ;-)
02-25-2010 05:37 PM
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BeNe Offline
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Post: #4
RE: Number of connections per IP / POP3
POP3 is a good option if your Mailbox quota is set to 10MB Big Grin
Or he use it to pull them on an Exchange Server in the internal Network, or for an Mailarchive. But i can´t find more reasons to use pop3 as you said.

Greez BeNe
02-25-2010 06:01 PM
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rbtux Offline
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Post: #5
RE: Number of connections per IP / POP3
well I would never choose a provider with quota below 1gig per mb...
02-25-2010 06:11 PM
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Zeitkind Offline
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Post: #6
RE: Number of connections per IP / POP3
Well, yes, POP3 is still good for fetching logs and such from several accounts belonging to several different servers, also mailing lists are still POP3 for me, just to keep the email-addresses separated in case the list gets hacked and spam floods the list (which happened earlier) and there is no need to store mailing lists on a mailserver.
People having this problem are all sysadmins or simular, also people fetching mail for several accounts (instead of using ETRN or relaying) to an internal mailserver. Most of them are stuck and wait for Apple to fix this issue, because they don't have the control over the mailserver.
Regarding ispcp - yes, it's a job for the sysadmin, not for resellers or users, because courier has only one global setting for that.
02-25-2010 06:58 PM
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kilburn Offline
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Post: #7
RE: Number of connections per IP / POP3
Quote:well I would never choose a provider with quota below 1gig per mb...

Amazing. I'm having a hard time trying to offer such high quotas for mailboxes, mainly because:

(1) Your mileage may vary, but my customers tend to retain each and every mail they've ever received, including multi-megabyte stupid powerpoint/video jokes and the like.
(2) Backing up *and* being able to quickly emergency-recover multiple (100+) gigabytes of data is not an easy thing to do given my server's limitations (100Mb/s connections). Backup problem: as the maildirs grow, the backup process changed files scan increases quickly (additional stats for each mail). SATA disks really hate processing millions of stat ops for individual files, so the thing turns into a slow beast unless I/O throttled which solves the issue but makes backups slower. Recovery problem: a simple calculation shows it: 100Mb/s ~ 44GB/hour (assuming an ideal network entirely dedicated to the restore process).

How do you handle these situations? Any ideas about them without throwing more/different hardware at it?

Additionally, IMAP clients usually keep open processes in the server. Obviously, people just leaves their mail clients open the whole day while they are working. This means that the number of open imap processes can easily grow to the hundreds, even thousands in busy hours. Do you want this happening to your servers?

Now you might tell me that I'm overloading my servers, but I have to strongly disagree. IMHO, the hardware requirements should grow mainly according to the numbers/bytes of mails received/sent, not to the number of mail accounts.
(This post was last modified: 02-25-2010 07:54 PM by kilburn.)
02-25-2010 07:48 PM
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rbtux Offline
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Post: #8
RE: Number of connections per IP / POP3
(02-25-2010 07:48 PM)kilburn Wrote:  
Quote:well I would never choose a provider with quota below 1gig per mb...

Amazing. I'm having a hard time trying to offer such high quotas for mailboxes, mainly because:

(1) Your mileage may vary, but my customers tend to retain each and every mail they've ever received, including multi-megabyte stupid powerpoint/video jokes and the like.

yeah so what ;-)) I do too... As long as the pay for it...

(02-25-2010 07:48 PM)kilburn Wrote:  (2) Backing up *and* being able to quickly emergency-recover multiple (100+) gigabytes of data is not an easy thing to do given my server's limitations (100Mb/s connections). Backup problem: as the maildirs grow, the backup process changed files scan increases quickly (additional stats for each mail). SATA disks really hate processing millions of stat ops for individual files, so the thing turns into a slow beast unless I/O throttled which solves the issue but makes backups slower. Recovery problem: a simple calculation shows it: 100Mb/s ~ 44GB/hour (assuming an ideal network entirely dedicated to the restore process).

How do you handle these situations? Any ideas about them without throwing more/different hardware at it?

we do backups for our Maildir with lvm snapshots (Maildir is on a separate LVM Partition...) and rsync. We have our own Racks and therefore gigabit network between the servers and the backbone, as well as a separate gigabit link for backup purposes only, so no big issues for us there... Even with 100Mbps the backup process should not make big pain (a full restore is an other story though...)

(02-25-2010 07:48 PM)kilburn Wrote:  Additionally, IMAP clients usually keep open processes in the server. Obviously, people just leaves their mail clients open the whole day while they are working. This means that the number of open imap processes can easily grow to the hundreds, even thousands in busy hours. Do you want this happening to your servers?

Well thats what the mailservers are for...
But I must say dovecot has a really small memory footprint each connection takes between 150k and 500k (swapable memory) on a decent server you can handle 500-1500 concurrent connections... (of course main limitation is i/o here..., but the idlers use almost nothing but memory)
[/quote]

(02-25-2010 07:48 PM)kilburn Wrote:  Now you might tell me that I'm overloading my servers, but I have to strongly disagree. IMHO, the hardware requirements should grow mainly according to the numbers/bytes of mails received/sent, not to the number of mail accounts.

yes you're right.


By the way I did attend an interessting talk with Timo Sirainen (the guy behind dovecot) last july and he has some really interessting plans for dovecot. He is working on storage separation of current and old mails.

That means you could serve the 50 most current mails for each user from SAS disk and the rest (archive) from a slower resource like sata, nas or even some sort of cloud filesystem (like amazon s3 or the like)

Also dovecot can act as imap proxy, so if you really have a lot of mailaccounts you can still provide a single point of access for your users, with multiple mailhosts in the backend...
here is the video and pdf of the talk I mentiond above:
http://www.heinlein-support.de/web/akade...ap-server/
(This post was last modified: 02-25-2010 09:47 PM by rbtux.)
02-25-2010 09:43 PM
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kilburn Offline
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Post: #9
RE: Number of connections per IP / POP3
Amazing conference! I really liked the "failback" storage idea, whereas I wasn't that impressed by the "cloud" speak nor the multi-mbox stuff (it takes advantadge of serial reads, but this is no longer necessary with ssd disks).

Memcached (or something similar) indexes + replicated fs over SSD disks for "newer" data + replicated fs over SATA for older data. That would be a dream! Wink

SuperThanks for the link (I'm looking at the Mark Martin's Amavisd tips next)!
(This post was last modified: 02-26-2010 02:16 AM by kilburn.)
02-26-2010 02:12 AM
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kartinkent Offline
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Post: #10
RE: Number of connections per IP / POP3
The purpose of Courier Configuration is so you can configure Courier via the WHM interface. Courier is used for POP3 on maildir systems and Courier-IMAP is used for IMAP on maildir systems.The reason for allowing more than one connection per IP is that many users on Cable and Dial-Up connections may share the same IP address.
03-23-2010 03:01 PM
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