[CentOS] Re: several servers

Luke S Crawford lsc at prgmr.com
Thu Jun 5 20:10:40 UTC 2008

roberto.barrientos at umag.cl writes:
> ok..i can install dovecot+postfix+MYSQL..etc..and maybe the problem it's
> resolve.
> i don't have problem with the machines, the machines are goods, my problem
> is the tranparent receive e-mails to the users than are distributed in
> four machines with the same number the users and different users in each.
> as does google??. they have one entry to e-mail system (gmail.com) but
> they have several machine (maybe thousands) in transparent mode.
> i read something like LVS...some comment about this software..! is my
> solution or I'm lost?
> Roberto.-

many ways to do this.  

The easiest option is to put customers on mail1.isp.com ... have
the server at isp.com just have a bunch of aliases pointing userx at isp.com
to userx at maily.isp.com  ... 

the disadvantages are that the end users need to know to set their
pop/imap clients to maily.isp.com, where y will be different for  different
users, and your aliases file will get big, and moving users from one
mailserver to another gets complicated (usually you put everyone on mail1
until it is almost full, then you put all new users on mail2, until it gets
full, etc...)  but incoming mail to user at isp.com will work, and this is by 
far the easiest to set up and it will scale pretty well.

at an ISP where I worked during the .com, we did this, but we wanted all 
users to go to mail.isp.com to get their mail.  we wrote a little C program 
that  listened on port 113 until the pop client issued 'user username'  and
then did a lookup (in the aliases file, incidentally... this got really
slow after we passed a million accounts-  I re-wrote it to use MySQL and 
things performed ok again)  to see where the user was and forwarded the 
rest of the pop3 session to the correct server.  Really this is a minor
tweak and only saves you the trouble of making your users know which mailserver
they need to connect to.

Finally, do a search on "Cyrus murder" essentially the cyrus mailserver 
includes support for clustering your mailservers.  It's not redundant 
(e.g. if you loose a physical server you can loose data) but it performs 
well, from what I hear. Cyrus is generally considered to be an 
'industrial strength' mailserver.

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