Unable to send Emails
Article ID: 107567
Updated On:
Products
Issue/Introduction
The Portal server IP has been added to the SMTP relay allow list. However we are unable to send any emails.
Environment
Cause
There was a conflict in subnet specification.
In this case the email server was in the range 10.0.1.X we found that the docker container could resolve the mail server name to the correct IP address, but that because docker was using the subnet 10.0.1.X it was not possible to route to the external 10.0.1.X mail server machine.
In setup of docker it is using internally three created networks -when we connect to the container trying to connect to the SMTP server :
Then run the route command :
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 172.18.0.1 0.0.0.0 UG 0 0 0 eth1
10.0.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
10.0.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth2
172.18.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1
Unfortunately one of them is the 10.0.1.X network, which blocks access to the external subnet 10.0.1.X, and hence blocks access to the mail server.
In the container, the DNS resolution works and we get the right IP for the mail server,
for i in `docker network ls | awk '{ print $1 }' `; do echo $i; (docker network inspect $i ); done
Resolution
In this case, the customer was able to setup SMTP server in another subnet.
Alternatively it may be possible to change the subnet used for the API Portal docker as per :
https://docops.ca.com/ca-api-developer-portal-enhanced-experience/4-2/en/install-configure-and-upgrade/troubleshoot-the-installation
This documents the setup of the 172.18.0.0 network, but may also be applicable to the 10.0.0.0 and 10.0.1.0 networks as well - in our case we did not need to go that far as we had an alternative.
Additional Information
# To find which image did the SMTP message : we used :
While
journalctl -f
will give trace of all the logs (assuming /etc/docker/daemon.json is setup correctly) - but it will not identify which container the logs come from.
Here we needed to find which container was making the SMTP call - so we did this :
for i in `docker ps | awk '{ print $1 }' `; do echo $i; (docker logs $i 2>&1 | grep SMTP); done
Gave us the container : 143701b52e37 as the container tryign to connect to the mail server.
143701b52e37
Jul 19 05:34:28 islandportal.example.com dockerd[27108]: WARNING: 4: Unable to send email: Unknown SMTP host: mail.example.com. Exception caught!
Then we could connect to that container :
docker exec -it 143701b52e37 sh
to print out the network and test resolving the SMTP host name:
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