Docker Image for Exim4
This is a simple Docker image for Exim4 based on the official alpine image.
Use it like this in your
version: "2" services: smtp: image: primesign/exim4 ports: - "25:25" volumes: - "./conf/exim4.conf:/etc/exim/exim.conf:ro" - "./conf/ssl/exim.crt:/etc/ssl/exim.crt:ro" - "./conf/ssl/exim.pem:/etc/ssl/exim.pem:ro" - "/var/opt/smtp/spool:/var/spool/exim" - "/var/opt/smtp/log:/var/log/exim"
Smart Host Configuration
To send email via a smart host disable the
dnslookup router in your
exim4.conf. And add a
smarthost router like follows:
smarthost: driver = manualroute domains = * transport = remote_smtp route_data = your.smart.host ignore_target_hosts = <; 0.0.0.0 ; 127.0.0.0/8 ; ::1 no_more
your.smart.host with the hostname or IP adress of your smart host (e.g. xxx.mail.protection.outlook.com in case of Office365 / Exchange Online).
For details see the official documentation.
SMTP TLS Client Authentication
In order to enable TLS authentication for the Exim SMTP client add
hosts_require_tls = * to your
remote_smtp transport configuration in your configuration file, and mount or add the corresponding certificate and private key files into your container.
remote_smtp: driver = smtp tls_certificate = /etc/ssl/exim.crt tls_privatekey = /etc/ssl/exim.pem hosts_require_tls = *
For details see 9. Configuring an Exim client to use TLS in the official Exim4 documentation.
When exim is compiled with GnuTLS the TLS client authentication only works if the server specifies a list of accepted issuer certificates (see this bug entry) - Exchange/Office365 does not. Therefore, we switched to Alpine since it's exim version is compiled with OpenSSL.