Zsombor B:
> Hi,
>
>
> I know this is a complicated question but what/where do you see
> possible bottlenecks in postfix?
> Is it CPU? RAM? Disk IO?
>
> I'm building an infra to send out ~3-5 million emails a day.
That might have been challenging 25 years ago. As Viktor notes,
the real challenge is to get receivers to accept your traffic at
these rates (besides not making mistakes on the sending side like
using a single-threaded submission channel).
For case studies in traffic management, see postfix-users mail from
the last 2-3 quarters about anything that involves outlook.com and
understand the recommendations that Viktor (and I) made there.
Recent examples:
- Postfix may exceed receiver concurrency limits when SMTP connection
reuse is enabled, and one SMTP transport is used for deliveries
to different providers. The workaround is to disable connection
reuse for that SMTP transport, or to use a dedicated SMTP transport
for a specific provider. The solution requires changes to Postfix's
connection cache management protocol.
- Postfix may exceed receiver concurrency limits when different
domains are hosted with the same provider. One solution is to use
check_recipient_mx_access plus "filter" to group these deliveries.
Other solutions require architectural changes to Postfix (looking
up next-hop MX information before scheduling deliveries)
Wietse
