Ram:
> I have a very busy postfix server that acts as a relay. It gets mails
> from an application and then forwards the mails to the delivery servers
> on local LAN
>
> The application can send mails at rate of? upto 600 mails per second
> Postfix has been configured to accept mails all that quickly, but the
> delivery is very poor until inflow stops. Only around 20-50 mails per s
> Once the app completes the inflow, then the mails are cleared at a rate
> of 1000 mails per second
>
> Why ?
>
> Is there a contention on the queue manager when the inflow is too quick ?
No, there is contention for the file system.
If you disabled in_flow_delay, turn it back on, please. This allows
the queue manager to push back, though it works only for clients
that make few parallel connections.
Otherwise, you need a faster disk. SSDs have become quite affordable,
even the 'enterprise' ones that have some extra capacitors to prevent
data corruption after power failure.
Wietse
