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How to activate TLS for Octeth Email Gateway Inbound SMTP Server

Octeth has a powerful, high-performance inbound SMTP server for the Email Gateway feature. This SMTP server accepts TLS connections as well. In order to activate TLS with a properly setup SSL certificate, follow these steps.

First, initiate your SSL certificate using Let’s Encrypt or other SSL certificate providers.

1. SSH into the oempro-app container:
Copy

cd /opt/oempro/
docker exec -ti oempro_app bash

2. Edit /var/www/html/_dockerfiles/inbound-smtp-server/server.key and set the file content to the private key of the new SSL certificate.
3. Edit /var/www/html/_dockerfiles/inbound-smtp-server/server.crt and paste the new (1) SSL certificate first, then (2) paste the CA bundle of the SSL certificate.
4. Edit /var/www/html/_dockerfiles/inbound-smtp-server/config.json and paste these two file paths to Certificate and PrivateKey parameters. Paths must be relative. Here’s an example:
Copy

{
  "Debug": false,
  "Listen": [
    ":25"
  ],
  "AppName": "Oempro SMTP Server",
  "Hostname": "test.local",
  "AdminAPIKey": "3b3c98-****-****-****-d3bb6b",
  "EmailMaxSizeKB": 100,
  "SMTPTimeout": 15,
  "Certificate": "./server.crt",
  "PrivateKey": "./server.key",
  "MaxConnectionLimit": 1500,
  "LogFiles": {
    "Connections": "./log_connections.log",
    "Authentications": "./log_authentications.log"
  },
  "OemproAPIUrl": "http://192.168.99.101/api.php"
}

5. Rebuild and re-delpoy the inbound SMTP server:
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cd /opt/oempro/
docker-compose build oempro_emailgateway_inbound_smtp
docker-compose kill oempro_emailgateway_inbound_smtp
docker-compose up -d oempro_emailgateway_inbound_smtp

6. Test the TLS connection:
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openssl s_client -quiet -starttls smtp -connect your.smtp-server.com:25 # (or 587)

depth=2 C = BE, O = GlobalSign nv-sa, OU = Root CA, CN = GlobalSign Root CA
verify return:1
depth=1 C = BE, O = GlobalSign nv-sa, CN = AlphaSSL CA - SHA256 - G2
verify return:1
depth=0 CN = *.sendlayer.net
verify return:1
250 ENHANCEDSTATUSCODES
ehlo local
250-smtp.sendlayer.net greets local
250-SIZE 307200
250-AUTH LOGIN PLAIN
250 ENHANCEDSTATUSCODES
quit
221 2.0.0 your.smtp-server.com Octeth SMTP Server v1.2 ESMTP Service closing transmission channel
read:errno=0

The server.crt file structure:

-----BEGIN CERTIFICATE-----
...
****************************************************************
****************************************************************
...
-----END CERTIFICATE----- 

-----BEGIN CERTIFICATE-----
...
****************************************************************
****************************************************************
...
-----END CERTIFICATE-----

The server.key file structure:

-----BEGIN PRIVATE KEY-----
...
****************************************************************
****************************************************************
...
-----END PRIVATE KEY-----

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• How to activate TLS for Octeth Email Gateway Inbound SMTP Server