Hello everyone,
I have a remote_smtp transport configured to send messages using the
same interface that originally received such message.
All is working well a part from one specific case: defers.
When messages are deferred due to termporary errors from the remote
hosts, it happens that after a while they are delivered using a
different interface, not the one that was previously designated.
After a long investigation, I noticed that it happens when the following
situation arises:
1. *msg1 *received from *interface1* and addressed to *hostA*.
2. *msg1 *delivery attempt using *interface1 *failed due to temporary
error of remote *hostA *(defer).
3. *msg2 *received from *interface2 *** and addressed to *hostA*.
4. *msg2 *delivery attempt using *interface2 *failed due to temporary
error of remote *hostA *(defer).
5. *msg3 *received from *interface3***** and addressed to *hostA*.
6. *msg3 *delivery attempt using *interface3 *successful (exim logs
mark the interface address on the "=>" line like this: I=[interface3]).
7. *msg1 *delivery attempt using *interface3 *successful (exim logs
mark the interface address on the "=>" line using a "*" like this:
I=[interface3]*).
8. *msg2 *delivery attempt using *interface3 *successful (exim logs
mark the interface address on the "=>" line using a "*" like this:
I=[interface3]*).
Exim knows that is using the wrong interface to deliver the messages,
because it puts a "*" near the interface in the logs!
Summarizing, the first interface that is able to deliver a message to a
host that has a retry time configured on other interfaces is used by
Exim to deliver every message that was previously deferred, with
disregard of the interface that was set at the transport level.
That, of course, is causing issues with SPF. The messages have to be
sent using the right interface (IP address)!
Is there a way to disable or control this behavior? It would also be a
useful feature it there was a way to select a fallback interface
following some configurable rules.
Thanks in advance for your help!
Matteo Bonora
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