Hi Russell, thanks for the answer. From: "Russell Coker" <russell@coker.com.au>

On Mon, 3 Jun 2013, Petros <Petros.Listig@fdrive.com.au> wrote:

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If I send many e-mails at the same time, I have a high number of re-delivery attempts because initially connections time out.

I am playing with some parameters in main.cf but haven't been very successful yet.

At the moment my main.cf says:

smtp_destination_rate_delay = 120s smtp_destination_concurrency_limit = 1 initial_destination_concurrency = 1 default_process_limit = 5

http://www.postfix.org/postconf.5.html#smtp_destination_concurrency_limit

smtp_destination_concurrency_limit is per recipient. So it will reduce the number of connections when sending to gmail and yahoo but not much else.

Yes. I would have liked one that would limit the number of outgoing SMTP connection globally but I could not find a parameter for it.

From the same URL the default_process_limit is the number of processes that the master process spawns, this will affect the DEFAULT for inbound connections but not much else.

Yep, seems so. Although it could be used to delay transfer from mailman to postfix, I thought. At the moment the recipient list is limited to 50 per connection (so mailman divides the list in chunks when sending mail). If I send it to 1 (default_process_limit = 1) it would restrict the number of recipients to 50 at the time, I think. I just don't know when mailman is sending the next chunk then (after one connection is closed?)

...

BTW: The server is in the Amazon EC2 cloud but I don't think it matters. Still, if I try a telnet on port 25, the connection opens faster from my office (ADSL) than from the Amazon VM.

Is there a reverse DNS issue?

Well, the reverse lookup resolves to ec2-...us-west-2.compute.amazonaws.com not to the used sender address because it is a dynamic address. At the moment I update it on internal DNS (I don't control the external) so if mail arrives at the company server it can redirect list mail to the Amazon computer.

EC2 should be fast enough. How many users are on the list?

Ca. 500 users. It is an announcement lists only. At the moment, I still have 56 mails left, after ca. 3 hours. It took ca. an hour to deliver the first 250. The main reason is "Connection time out", according to mailq. The mail itself is a PDF with less than one 1 Mbyte. I am surprised by the slowness. I wonder whether Amazon is throttling SMTP traffic. We have our mail server inhouse, and having the list server inhouse is clogging the ADSL connection. So I try Amazon, I thought. We do not own rack space otherwise I would have done it in a datacentre. Regards Peter