Hello Wietse, Thanks for your reply.
My reading of your answer is, that by default, if some recipients are accepted and others 451/452 rejected, postfix closes the SMTP session, reopens a new SMTP session to the same host and tries again to that host (smtp_mx_session_limit default 2). With the remaining recipients, postfix opens a session to another IP address, extracted from DNS/MX and repeats the procedure, by trying by smtp_mx_address_limit (default: 5) times. That is, for a message with 11 recipients, if the SMTP accepts one recepient per SMTP transaction and defers the others recipient, for a domain having 50 different IP addresses, postfix will deliver the mail to the first ten recipients almost at the same time, and delivery to the 11th recipient will be postponed to whenever postfix is configured to retry. The further, my reading is that postfix does not evaluate 4.5.3 anyhow special for determining the retry strategy. Regards Дилян On Mon, 2019-07-29 at 10:02 -0400, Wietse Venema wrote: > > If a site publishes many MX records pointing to the same IP address, > > will Postfix do a lot of tries (reducing the amount of pending > > recipients in each iteration) in shortes time? > > When a recipient fails with 4xx, Postfix does not give up immediately, > but will try the remaining MX hosts, up to the limits specified > with $smtp_mx_address_limit and $smtp_mx_session_limit. > > Wietse
