Brandon Hilkert:
> We send out a pretty volume of emails right now using a combination
> of SQL and IIS SMTP. We get rates now of about 5,000/min. We're
> looking to not only improve the rates, but incorporate DKIM/Domainkey
> signing into the process. The choice has been made to go with
> postfix along with a queue directory on an XFS file system.
>
> I'm using postfix as a relay, and having it sign the outgoing
> emails with DKIM. That process was about twice as slow as without
> it. Without DKIM, I'm getting a rate of 700/min.
>
> I was expecting much better performance out of the box. I realize
> in my tests I'm going from a single host, to another single postfix
> box that is receiving all the emails to one account, so there may
> be bottlenecks that exist in my test setup, that may not be there
> in our production environment.
>
> I'm really hoping to move away from MS SMTP and don't have tons
> of experience with Linux, so I'm hoping people could give me some
> good ideas about improving outbound performance. The server will
> not be directly exposed to the internet, so security is less of
> a concern as it will be behind several Cisco firewalls. This server
> will not be receiving any email, so nothing needs to be considered
> for that side.
To improve performance, you need to identify the bottleneck.
Usually, the file system is the slowest component.
On Linux systems, fixing this can be as simple as editing the
syslog.conf file and making sure that the syslog daemon does not
sync the disk after every logfile record. Something like:
mail.* -/var/log/maillog
Postfix was recently clocked at several thousand messages a second
while sending mail, but receiving mail is much more expensive since
each message needs to be made persistent on the local disk.
You also need to keep in mind that you can't deliver mail as fast
to ONE single machine as you can deliver to the whole Internet.
In the one machine case, all the mail is fighting for access to
the same file system, while with mail into the Internet, you are
effectively spreading the load over many remote file systems.
Wietse
