concerning dovecot settings for high volume server

[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
>