> On Mar 3, 2019, at 2:56 AM, Ronald F. Guilmette <r...@tristatelogic.com> > wrote: > > But this other fellow I've been taking to offered an unexpected observation: > If a given Postfix installation was attempting to support, say, 1 million > unique domain names (correponding to 1 million unique customers) and if > just 11,000 of those were to all simultaneously attempt to send -outbound- > emails to six (6) different destinations apiece, then... this other fellow > asserted... all of the 65536 maximum available IPv4 port numbers would be > exhausted, and then havoc would ensue.
This mental model is deeply flawed. Postfix has a queue manager, that limits the concurrency per destination, and the active queue size. And a master(8) process that limits the process count per transport. Postfix also accepts messages at a finite rate, so 66,000 messages will not arrive instantaneously. Once the active queue is full further accepted messages will accumulate in the incoming queue on disk, but will not consume network resources or RAM. It is of course possible to receive inbound messages faster than the steady-state output rate, in which case the number of queued messages will grow quite high. And if this is allowed to continue indefinitely, until the file system almost fills up. But the port number exhaustion scenario is not even close. http://www.postfix.org/OVERVIEW.html#delivering http://www.pos -- Viktor.
