On Fri, 30 Nov 2012, lst_ho...@kwsoft.de wrote:
Zitat von Tomas Macek <ma...@fortech.cz>:
On Fri, 30 Nov 2012, lst_ho...@kwsoft.de wrote:
Zitat von Tomas Macek <ma...@fortech.cz>:
I don't understand now, how Postfix behaves when listenting on submission
port 587.
Our mailserver is sometimes overloaded on port 25, so we want to use
postscreen. But I don't understand, how Postfix works when it's stressed
on port 587, when spammers connect to that opened port and want send
their "emails". In document http://www.postfix.org/STRESS_README.html
there is:
NOTE: To avoid "overload" delays for end-user mail clients, enable the
"submission" service entry in master.cf (present since Postfix 2.1), and
tell users to connect to this instead of the public SMTP service.
Should this mean, that Postfix by default does not use counters like
smtpd_hard_error_limit, smtpd_junk_command_limit and maybe others on
sumission port? On this port I would prefer using some kind of smtp auth
and this port should be world accessible to allow the clients using other
networks to authenticate and send emails.
Port 587 is by default nothing special for Postfix because it is mostly a
clone of the Port 25 service. The *intended* difference is that Port 587
should only accept mail by authenticated users, so no chance for spammers
if they don't own valid credentials. To actually see the difference
between Port 25 and Port 587 settings you have to compare the entries in
master.cf.
Regards
Andreas
OK, so there is a chance for spammers to overload the server using
submission port 587 (the server says then "service "smtp" (25) has
reached its process limit "200"") by exhausting number of available ports
and the MUA clients then can have also problems to send their
emails? I'm I right?
The number of available ports is a OS thing, Postfix can be configured in
master.cf the not allow more than maxproc-column service processes *per
service*. So if you have 200 maxproc for Port 25 and another 200 for Port 587
your OS must be able to handle at least 400 connections (open ports, fds
etc.). If 200 are reached at Port 25 Postfix will still accept up until 200
connections on Port 587, but refuses any further connections on Port 25.
According to the doc:
It works as follows. When a "public" network service such as the SMTP
server runs into an "all server ports are busy" condition, the Postfix
master(8) daemon logs a warning, restarts the service (without
interrupting existing network sessions), and runs the service with "-o
stress=yes" on the server process command line:
Just see "all server ports are busy": what means the "ports"? Because I
experieced the stress=yes at smtpd processes, when just 121 smtpd
processes were running that time.
If I'm, then I don't understand, why to split the processes into submission
587 and normal 25, because if the MUA client send the mail
through 25 (hope with postscreen), there is a chance that the 25 is not
overloaded (because it uses postscreen) and he will be rather
able to send his email compared to 587.
Or I don't still understand something ... :-)
No, MUA should use Port 587 and *authentication*. Port 25 is for MTA <--->
MTA transfer *without* authentication. It does work to use Port 25 with MUA
but it is not recommended these days. Postscreen is able to prevent some
spammer connections to actually allocate one of this 200 port 25 processes so
the boundery is higher but still applies.
Andreas
Yes, I understand this well and know about it and this is what I want. But
don't undrestand howto avoid overloading the server, when spammers will
try to connect and send their mails to the port 587.
If the Postfix's behaviour on port 587 is the same as with 25, it seems to
me to be better to let the MUAs to send their mail to 25. In the
postscreen the mynetworks are automatically whitelisted and on 25 they
have better chance to send their mails, because 25 should not be
overloaded because of postscreen used.
Using firewall on 587 is useless, because our clients travel with their
computers even around Europe and want to send their mails.
Toamas