imagine, a mail envolope contains many recipient, The server accepts the first recipients and rejects the last
recipients, meaning “Too many recipients in this transaction”.
RFC 821 specifies the reply code 452 as “Insufficient storage”, which RFC 5821 amends, by stating that 452 can mean also
too many recipients in this transaction.
RFC 3463 defines enhanced status code 4.5.3 stating “Too many recipients”. RFC 5248 attaches the ESC 4.5.3 to reply
code 451, stating that changing this binding requires a specification, and there is no such specificaton. The latter
means, that 452 4.5.3 is not valid.
Looking only on the source code Postfix 3.4.6 and sendmail 8.16.0.41 send “452 4.5.3 Error: too many recipients”. Exim
sends just “452 too many recipients”.
How can Exim be tweaked to retry immediately:
• Does Exim interpret 4.5.3 anyhow special?
• Does it handle 451 and 452 differently by default?
• If a site publishes many MX records pointing to the same IP address, will Exim do a lot of tries (reducing the
amount of pending recipients in each iteration) in shortes time?
• If a site published one MX records pointing to many different IPv6 addresses, will Exim do a lot of retries to
deliver the same message in shortest time?
I guess, that a site publishing many MX records pointing to many IP addresses is not an additional option to increase
the retry rate.
