Connection refused to 127.0.0.1:587 when email sending

[DIG-Tofu]

Hi guys,

I'm contacting you about an issue currently encountered on my wireguard-ui container.

When I would like to send an email with the WG configuration of my user, I receive the following error :
"Mail Error on dialing with encryption type STARTTLS: dial tcp 127.0.0.1:587: connect: connection refused"

I've attached my docker run command in bottom of the description if needed.

I've questions about that :
Why the container need to reach his loopback address with SMTP protocol ?
I've tried with gmail first but seems working well when i'm doing telnet tests.
I've moved to SendGrid to check if the behavior is the same and it is.

I've dig a lot of topic about this issue but I found anything. Even some AIs don't have the right answer (yeah I've asked to OpenAI...).

sudo docker run -d --name wireguard-ui
--restart=unless-stopped
-p 51820:51820/udp
-p 51821:51821
-p 5000:5000
-v wg-data:/my/own/volumes/wg
-e WG_HOST=192.168.1.100
-e SMTP_HOST=127.0.0.1
-e SMTP_PORT=587
-e SMTP_USERNAME=apikey
-e SMTP_PASSWORD=MY_API_KEY
-e SMTP_FROM=d*****@gmail.com
-e SMTP_FROM_NAME="WireGuard Config"
-e SMTP_ENCRYPTION=starttls
ngoduykhanh/wireguard-ui

Hope it will help.

Best regards,

[b2un0]

in a docker container the loopback interface is the docker container self.

inspect the docker default bridge network interface and use the gateway IP as SMTP_HOST, mostly 172.17.0.1

docker network inspect bridge | grep Gateway

[DIG-Tofu]

in a docker container the loopback interface is the docker container self.

inspect the docker default bridge network interface and use the gateway IP as SMTP_HOST, mostly 172.17.0.1

docker network inspect bridge | grep Gateway

I've removed the ENV variable SMTP_HOST and I've tried the following docker run command :

The mail seems to be well sent, but when I'm trying to verify the integration with my sendgrid API, it fails, by default I don't receive the mail.

sudo docker run -d
--name wireguard-ui
--restart=unless-stopped
-p 51820:51820/udp
-p 51821:51821
-p 5000:5000
-v wg-data:/home/dosel/dockvolumes/wg
-e WG_HOST=192.XXX.XXX.XXX (IP of the docker server)
-e SENDGRID_API_KEY=SG.xxxxx
-e SMTP_HOST=smtp.sendgrid.net
-e SMTP_PORT=587
-e SMTP_FROM=d********@gmail.com
-e SMTP_FROM_NAME="WireGuard Config"
-e SMTP_ENCRYPTION=starttls ngoduykhanh/wireguard-ui

It seems to be reliable but maybe I've missed a specific variable.

In any cases, thanks by advance for you help.

Tofu