# Connecting to a SMTP server on localhost:25 without auth?
**URL:** https://meta.discourse.org/t/connecting-to-a-smtp-server-on-localhost-25-without-auth/156849
**Category:** Self-hosting
**Tags:** email
**Created:** [November 7, 2019, 1:32pm UTC](https://meta.discourse.org/t/connecting-to-a-smtp-server-on-localhost-25-without-auth/156849 "2019-11-07T13:32:21Z")
**Posts on this page:** 1
**Showing post:** 3
### Author:  [@maltfield](https://meta.discourse.org/u/maltfield)
#### Post date: [November 25, 2019, 10:27am UTC](https://meta.discourse.org/t/connecting-to-a-smtp-server-on-localhost-25-without-auth/156849/3 "2019-11-25T10:27:11Z")
> [@pfaffman](#):
>
> I think that hasn’t been very true for about 20 years.
In 2019, it’s the default config for postfix on RHEL/CentOS. Postfix binds only to the loopback interface and drops all smtp requests that don’t originate from `127.0.0.0/8`. No auth required. I’m not sure about debian, but I’d _imagine_ `exim` has a similar default config.
A couple relevant topics on these forums from other users who hit this issue:
- [How to set SMTP config to use localhost?](https://meta.discourse.org/t/how-to-set-smtp-config-to-use-localhost/131464)
- [https://meta.discourse.org/t/smtp-without-user-or-password/88879](https://meta.discourse.org/t/smtp-without-user-or-password/88879)
There doesn’t appear to be a topic for how to set this up on RHEL/Cent OS with the necessary changes to both Discourse _and_ postfix, so I’m documenting this here.
This does not appear to be possible with the `discourse-setup` script, but I did get this to work.
First, I had to figure out the IP address of the docker host as the docker container sees it. Using `127.0.0.1` won’t work because the docker container will see `127.0.0.1` as _itself_. Rather, we need to specify the IP address or hostname of the docker _host_ that is running the postfix SMTP server, and one that is addressible by the docker container (so not your docker host’s Internet-facing IP address if you want your SMTP server to not be Internet-accessible, for example).
I extracted the relevant IP address of the docker host (`172.17.0.1`) from the `docker0` interface by executing this on the docker host:
```plaintext
[maltfield@osestaging1 ~]$ ip address show docker0
3: docker0: mtu 1500 qdisc noqueue state UP
link/ether 02:42:80:35:65:a1 brd ff:ff:ff:ff:ff:ff
inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
valid_lft forever preferred_lft forever
inet6 fe80::42:80ff:fe35:65a1/64 scope link
valid_lft forever preferred_lft forever
[maltfield@osestaging1 ~]$
```
Then I edited my Discourse app’s yaml file, setting the “DISCOURSE\_SMTP\_ADDRESS” to `172.17.0.1` from above.
```plaintext
[maltfield@osestaging1 ~]$ cd /var/discourse/
[maltfield@osestaging1 discourse]$ grep SMTP containers/app.yml
DISCOURSE_SMTP_ADDRESS: 172.17.0.1
DISCOURSE_SMTP_PORT: 25
DISCOURSE_SMTP_AUTHENTICATION: none
DISCOURSE_SMTP_OPENSSL_VERIFY_MODE: none
DISCOURSE_SMTP_ENABLE_START_TLS: false
[maltfield@osestaging1 discourse]$
```
Note that I first tried to use the internal docker hostname `host.docker.internal` for this, but apparently this hostname isn’t available to linux docker users
- [Support host.docker.internal DNS name to host · Issue #264 · docker/for-linux · GitHub](https://github.com/docker/for-linux/issues/264)
Because the default postfix configuration in RHEL/Cent OS binds only to 127.0.0.1 (which is good), you’ll need to change `/etc/postfix/main.cf` so it also binds to the `docker0` interface and add that subnet to the `mynetworks` group so that SMTP traffic coming from docker containers will be accepted by postfix.
```plaintext
[maltfield@osestaging1 postfix]$ grep -ir '172.17' /etc/postfix/*
/etc/postfix/main.cf:inet_interfaces = 127.0.0.1, 172.17.0.1
/etc/postfix/main.cf:mynetworks = 127.0.0.0/8, 172.17.0.0/16
[maltfield@osestaging1 postfix]$
```
After those changes, rebuild Discourse and it should now be able to send emails out through your docker host’s postfix.
```plaintext
/var/discourse/launcher rebuild app
```
While this works, I have a few questions:
1. Is there some other environment variable or hostname that already points to the docker host (`172.17.0.1` in this case)?
I noticed that there is a [DISCOURSE\_HOST\_IP](https://github.com/discourse/discourse_docker/blob/d775b4623752b7c53e1e98784ae39109a25a5b25/launcher#L103) environment variable “injected” by `launcher`. Is it possible to set this `DISCOURSE_SMTP_ADDRESS` yaml key to the same value as the other’s yaml key with something like this?
```plaintext
DISCOURSE_SMTP_ADDRESS: $DISCOURSE_HOST_IP
```
1. In general, how durable is the `172.17.0.1` IP of the docker host? Is it always this IP on RHEL/Cent OS systems? Will it ever change on me?
---
_[View the full topic](https://meta.discourse.org/t/connecting-to-a-smtp-server-on-localhost-25-without-auth/156849)._