concerning dovecot settings for high volume server

Mon Sep 14 07:47:50 UTC 2015

Hi Rajesh,

our setup looks as follows:

- we are running linux-vserver as virtualization technology
- we have 2 dedicated IMAP/POP3 Proxies in front of 8 dovecot containers.
- totally about 2900 concurrent imap sessions on each imap proxy and about 180 concurrent pop3 sessions

- all dovecot containers are running on the same hardware (no problems until today):
	DELL PER720 with 2x 200GB RAID 1 SSD's for dovecot indexes, 8x 4TB RAID 10 for maildata, 2x300GB RAID1 for OS
	64GB RAM, 2x CPU E5-2640 0 @ 2.50GHz

- HA is Active/Passive with DRBD on 10GBIT dedicated NIC's for all 3 partitions.
- in summary there are about 47k accounts on it.
- 15minutes system load is between 0.5 - 2.5

- mailserver software is always postfix
- amavis with spamassassin and clamav
- opendkim, opendmarc as milter implementations

Front MX and antispam filtering is running on 2 different machines. Mail volume is between 200k and 600k (spam inclusive) per day.
We never faced some email re-download, only if the customers changes his mail client. But that's normal.

Hope that helps.

Best
Urban

Am 13.09.2015 um 19:35 schrieb Rajesh M:
> thanks very much urban. this was very helpful.
> 
> i have around 12500 users spread over 3 independent servers each having around 4000+ users
> i am using qmailtoaster, vpopmail, spamassassin and dovecot.
> 
> in future i am planning to consolidate all using a HA cluster.
> 
> if it is ok with you could you kindly share some information about your email server configuration. if you do not wish to put it on the list then you can directly email me.
> 
> 1) is your email volume high ?
> 2) server hardware to support  28000 users
> 3) mailserver software - exim or postfix ??.
> 4) antispam software like spamassassin if any
> 
> also if you have faced any email re-download issues with dovecot sometimes randomly incase of pop3 users storing emails on the server ?
> 
> 
> thanks
> rajesh
> 
> 
> 
> ----- Original Message -----
> From: Urban Loesch [mailto:bind at enas.net]
> To: dovecot at dovecot.org
> Sent: Sun, 13 Sep 2015 09:33:14 +0200
> Subject: Re: concerning dovecot settings for high volume server
> 
> Hi,
> 
> I have running dovecot with about 28k users.
> Here comes my relevant config for pop3 and imap from "doveconf -n".
> No problems so far.
> 
> -- snip --
> default_client_limit = 2000
> ...
> 
> service imap-login {
>    inet_listener imap {
>      port = 143
>    }
>    process_limit = 256
>    process_min_avail = 50
>    service_count = 1
> }
> service imap {
>    process_limit = 2048
>    process_min_avail = 50
>    service_count = 1
>    vsz_limit = 512 M
> }
> ...
> 
> service pop3-login {
>    inet_listener pop3 {
>      port = 110
>    }
>    process_limit = 256
>    process_min_avail = 25
>    service_count = 1
> }
> service pop3 {
>    process_limit = 256
>    process_min_avail = 25
>    service_count = 1
> }
> ...
> 
> protocol imap {
>    imap_client_workarounds = tb-extra-mailbox-sep
>    imap_id_log = *
>    imap_logout_format = bytes=%i/%o session=<%{session}>
>    mail_max_userip_connections = 40
>    mail_plugins = " quota mail_log notify zlib imap_quota imap_zlib"
> }
> 
> ...
> protocol pop3 {
>    mail_plugins = " quota mail_log notify zlib"
>    pop3_logout_format = bytes_sent=%o top=%t/%p, retr=%r/%b, del=%d/%m, 
> \ size=%s uidl_hash=%u session=<%{session}>
> }
> -- snip --
> 
> Regards
> Urban
> 
> 
> Am 12.09.2015 um 20:53 schrieb Rajesh M:
>> hi
>>
>> centos 6 64 bit
>>
>> hex core processor with hyperthreading ie display shows 12 cores
>> 16 gb ram
>> 600 gb 15000 rpm drive
>>
>> we are having around 4000 users on a server
>>
>>
>> i wish to allow 1500 pop3 and 1500 imap connections simultaneously.
>>
>> need help regarding the settings to handle the above
>>
>> imap-login, pop3-login
>> imap pop3 service settings
>>
>> i recently i got an error
>> imap-login: Error: read(imap) failed: Remote closed connection (process_limit reached?)
>>
>>
>> my current dovecot config file
>>
>> # 2.2.7: /etc/dovecot/dovecot.conf
>> # OS: Linux 2.6.32-431.23.3.el6.x86_64 x86_64 CentOS release 6.5 (Final)
>> auth_cache_negative_ttl = 0
>> auth_cache_ttl = 0
>> auth_mechanisms = plain login digest-md5 cram-md5
>> default_login_user = vpopmail
>> disable_plaintext_auth = no
>> first_valid_gid = 89
>> first_valid_uid = 89
>> log_path = /var/log/dovecot.log
>> login_greeting = ready.
>> mail_max_userip_connections = 50
>> mail_plugins = " quota"
>> managesieve_notify_capability = mailto
>> managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date ihave
>> namespace {
>>    inbox = yes
>>    location =
>>    prefix =
>>    separator = .
>>    type = private
>> }
>> passdb {
>>    args = cache_key=%u webmail=127.0.0.1
>>    driver = vpopmail
>> }
>> plugin {
>>    quota = maildir:ignore=Trash
>>    quota_rule = ?:storage=0
>> }
>> protocols = imap pop3
>> service imap-login {
>>    client_limit = 256
>>    process_limit = 400
>>    process_min_avail = 4
>>    service_count = 0
>>    vsz_limit = 512 M
>> }
>> service pop3-login {
>>    client_limit = 1000
>>    process_limit = 400
>>    process_min_avail = 12
>>    service_count = 0
>>    vsz_limit = 512 M
>> }
>> ssl_cert = </var/qmail/control/servercert.pem
>> ssl_dh_parameters_length = 2048
>> ssl_key = </var/qmail/control/servercert.pem
>> userdb {
>>    args = cache_key=%u quota_template=quota_rule=*:backend=%q
>>    driver = vpopmail
>> }
>> protocol imap {
>>    imap_client_workarounds = delay-newmail
>>    mail_plugins = " quota imap_quota"
>> }
>> protocol pop3 {
>>    pop3_client_workarounds = outlook-no-nuls oe-ns-eoh
>>    pop3_fast_size_lookups = yes
>>    pop3_lock_session = no
>>    pop3_no_flag_updates = yes
>> }
>>
>>
>> thanks very much,
>>
>> rajesh
>>
> 