Hi,
Rainer Dorsch via Exim-users <exim-users@???> (Sa 13 Apr 2019 18:15:33 CEST):
> I want to upgrade my server from Debian Jessie to Debian Stretch. I am afraid
> that at some time during the upgrade process, there is an invalid exim
An invalid Exim (or configuration) should not cause messages to get
lost.
If Exim can't start because of an invalid config, nobody can send you a
message, they will retry later.
If Exim can't acknowlege the message reception (due to runtime problems,
in the ACL), it will tmp reject the message, the sender will retry it.
If Exim can't route/transport the message (because of an invalid
configuration), *after* Exim acknowledged the message to the sender,
Exim will freeze that message and you can handle the problem.
Of course, there are more scenarios, where messages will get lost. But
Exim is fairly robust against such scenarios. Biggest problem are
logical errors, that are no configuration errors. But this is unlikly to
happen, if you've a working config.
The Exim maintainers are careful in retaining compatibility with
configurations written for previous releases.
> configuration and messages get rejected. In order to avoid that I was thinking
> of either redirecting via DNS to a server which does not listen to port 25 to
> enforce the sender to try again. Or redirect via DNS to a server which buffers
> all incoming messages until the Stretch setup is tested (not sure which server
> software does this though...).
Just block (DROP) incoming traffic on Port 25 and do some testing from
IPs you do not block. Or use swaks for ACL testing, use exim -N, exim
-bv, exim -bt for testing.
Redirecting messages to another server may impose more problems,
depending on how this fallback server handles the mail it queued. (E.g.
SPF may be broken for SPF protected domains, if the fallback now
delivers the messages to your box)
Best regards from Dresden/Germany
Viele Grüße aus Dresden
Heiko Schlittermann
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