Configuring a smtp_relays does not honor the routing table.

[cvillabrille]

Describe the bug

Configure a smtp_relays server in postal.yml, and some domains in the routing section.

Sending and email with multiple recipients, if the first email in To is external (not included in the routing), Postal does not honor the routing table and forward the delivery of the email of all recipients to the relay_host, and does not attempt to deliver the domains configured in the routing section.

A clear and concise description of what the bug is.

Configuring:

• smtp_relays with a valid relay server (relay.somedomain.com)
• domain1.com routing to smtp.domain1.com
• domain2.com, routing to smtp.domain2.com

One email sent to :
[email protected]; [email protected]; [email protected].
Postal will honor the routing and forward the email to domain1.com, domain2.com and gmail.

However, if the first emails in To: is an external email (to be forwarded to the relay, i.e. gmail), all the delivery is forwarded to the relay server, including those (domain1 and domain2) configured as routing. Postal does not try to delivery domain1.com and domain2.com by itself.

To Reproduce

1. Configure the smtp_relays value in postal.yml.
2. Add a routing to domain1.com with a valid smtp server.
3. Prepare an email to: [email protected] ; [email protected]
4. Email to [email protected] is not delivered by Postal but sent to the smtp_relays server since the first email in the list is external.
5. While if you set first [email protected] ; [email protected], the email to domain1.com is delivered by postal and the one to Gmail is forwarded to the relay_host.

Expected behaviour

Honor the routing does not matter which is the first email in To:

A clear and concise description of what you expected to happen.

Does not matter which email address is set the first. Postal must check if the email is to be sent to the relay server and for those configured in the routing section, try to deliver the email to those domains.

Environment details

• OS: Ubuntu 24
• Postal version: latest

[willpower232]

I don't think smtp_relays does anything other than send all email from Postal via a specific channel, I don't think it has the logic you're thinking of in it.

[cvillabrille]

Hi Will,

thanks for the reply.

That's the weird thing here. The point is, if I change the order and the domain1.com or domain2.com (that I have a routing definition) are the first email in the To: list, Postal has that logic and attempt to delivery to domain1.com, domain2.com and the rest addresses to the relay_host.

Only if I start the To: list an email considered as "relay" then is when it does not attempt to delivery domain1.com and domain2.com, just forward and let all the responsibility to the relay_host.

Weird, isn't?

[cvillabrille]

Other suggestion?

I have logs and plenty of tests on this behavior.

If I set the external email first in the list, the internal domains (domain1 and domain2 in this example, which are not accessible from the smtp_relays host) are not delivered since are forwarded to the smtp_relays host with no access to domain1 and domain2...

On the other hand, when the email address that should be forwarded to the smtp_relays hosts is set at any position (i.e 2nd, 3rd) all the emails arrive until we reach the external address. Any email address added after, does not arrive.

Hence, Postal does not honor the routing for those address set after one using a smtp_relays host.

[cvillabrille]

To add a bit of more information.

Logs of the worker when we send an email with the following To: list. (example 1 of the above list)

mutt -s "Test email" "[email protected]; [email protected]; [email protected]"

starting message unqueue component=worker thread=work1 original_queued_message=354
queue latency is 3.131274461746216s component=worker thread=work1 original_queued_message=354
parsing message content as it hasn't been parsed before component=worker thread=work1 original_queued_message=354 queued_message=354
Connected to 50.51.52.53:25 (smart_host.forwarder.com) log_id=CWIYT3C8 component=worker thread=work1 original_queued_message=354 queued_message=354
Sending message 1::333 to [email protected] log_id=CWIYT3C8 component=worker thread=work1 original_queued_message=354 queued_message=354

starting message unqueue component=worker thread=work0 original_queued_message=355
queue latency is 3.9189493656158447s component=worker thread=work0 original_queued_message=355
parsing message content as it hasn't been parsed before component=worker thread=work0 original_queued_message=355 queued_message=355

Accepted by 50.51.52.53:25 (smart_host.forwarder.com) for [email protected] log_id=CWIYT3C8 component=worker thread=work1 original_queued_message=354 queued_message=354
message processing complete component=worker thread=work1 original_queued_message=354 queued_message=354
finished message unqueue component=worker thread=work1 original_queued_message=354

starting message unqueue component=worker thread=work1 original_queued_message=356
queue latency is 3.9644083976745605s component=worker thread=work1 original_queued_message=356
parsing message content as it hasn't been parsed before component=worker thread=work1 original_queued_message=356 queued_message=356
Connected to 50.51.52.53:25 (smart_host.forwarder.com) log_id=FJYW5ZNT component=worker thread=work0 original_queued_message=355 queued_message=355
Sending message 1::334 to [email protected] log_id=FJYW5ZNT component=worker thread=work0 original_queued_message=355 queued_message=355
Connected to 50.51.52.53:25 (smart_host.forwarder.com) log_id=AKE9T9KD component=worker thread=work1 original_queued_message=356 queued_message=356
Sending message 1::335 to [email protected] log_id=AKE9T9KD component=worker thread=work1 original_queued_message=356 queued_message=356
Accepted by 50.51.52.53:25 (smart_host.forwarder.com) for [email protected] log_id=AKE9T9KD component=worker thread=work1 original_queued_message=356 queued_message=356
message processing complete component=worker thread=work1 original_queued_message=356 queued_message=356
finished message unqueue component=worker thread=work1 original_queued_message=356
Accepted by 50.51.52.53:25 (smart_host.forwarder.com) for [email protected] log_id=FJYW5ZNT component=worker thread=work0 original_queued_message=355 queued_message=355
message processing complete component=worker thread=work0 original_queued_message=355 queued_message=355

Logs of the worker when we send an email with the following To: list. (example 3 of the above list)

mutt -s "Test email" "[email protected]; [email protected]; [email protected]"

starting message unqueue component=worker thread=work1 original_queued_message=357
queue latency is 2.6448798179626465s component=worker thread=work1 original_queued_message=357
message is incoming component=worker thread=work1 original_queued_message=357 queued_message=357
inspecting message component=worker thread=work1 original_queued_message=357 queued_message=357
message inspected, headers added spam_score=0 component=worker thread=work1 original_queued_message=357 queued_message=357
Connected to 10.11.12.1:25 (smtp.domain1.com) log_id=JFZOJQAA component=worker thread=work1 original_queued_message=357 queued_message=357
Sending message 1::336 to [email protected] t log_id=JFZOJQAA component=worker thread=work1 original_queued_message=357 queued_message=357
Accepted by 10.11.12.1:25 (smtp.domain1.com) for [email protected] log_id=JFZOJQAA component=worker thread=work1 original_queued_message=357 queued_message=357
message processing completed component=worker thread=work1 original_queued_message=357 queued_message=357
finished message unqueue component=worker thread=work1 original_queued_message=357

starting message unqueue component=worker thread=work1 original_queued_message=358
queue latency is 2.803494453430176s component=worker thread=work1 original_queued_message=358
message is incoming component=worker thread=work1 original_queued_message=358 queued_message=358
inspecting message component=worker thread=work1 original_queued_message=358 queued_message=358
message inspected, headers added spam_score=0 component=worker thread=work1 original_queued_message=358 queued_message=358
Connected to 20.21.22.23:25 (smtp.domain2.com) log_id=5OQKBKCZ component=worker thread=work1 original_queued_message=358 queued_message=358
Sending message 1::337 to [email protected] log_id=5OQKBKCZ component=worker thread=work1 original_queued_message=358 queued_message=358
Accepted by 20.21.22.23:25 (smtp.domain2.com) for [email protected] log_id=5OQKBKCZ component=worker thread=work1 original_queued_message=358 queued_message=358
message processing completed component=worker thread=work1 original_queued_message=358 queued_message=358
finished message unqueue component=worker thread=work1 original_queued_message=358

starting message unqueue component=worker thread=work1 original_queued_message=359
queue latency is 2.9426372051239014s component=worker thread=work1 original_queued_message=359
parsing message content as it hasn't been parsed before component=worker thread=work1 original_queued_message=359 queued_message=359
Connected to 50.51.52.53:25 (smart_host.forwarder.com) log_id=3VXLPSFS component=worker thread=work1 original_queued_message=359 queued_message=359
Sending message 1::338 to [email protected] log_id=3VXLPSFS component=worker thread=work1 original_queued_message=359 queued_message=359
Accepted by 50.51.52.53:25 (smart_host.forwarder.com) for [email protected] log_id=3VXLPSFS component=worker thread=work1 original_queued_message=359 queued_message=359
message processing complete component=worker thread=work1 original_queued_message=359 queued_message=359
finished message unqueue component=worker thread=work1 original_queued_message=359

We have tested with :
batch_queued_messages: false

and also with :
batch_queued_messages: true