How to Send Email from Docker: A Guide to SMTP and API Methods

Docker containers do not send email directly, but Dockerized PHP applications can deliver messages through an external service such as Mailtrap using either SMTP or an email API. The guide explains how to configure Mailtrap credentials, install and configure PHPMailer, optionally enable OpenSSL for TLS or SSL, build PHP container images with Dockerfiles, and use Docker Compose plus environment variables sourced from Bash scripts to keep credentials out of application code. It provides examples for sending plain-text and HTML messages, attachments, and messages to multiple direct, CC, and BCC recipients through SMTP, while the API approach uses PHP cURL requests, bearer-token authentication, JSON payloads, and Base64-encoded attachments. It also outlines how to start, enter, and stop containers and troubleshoot common problems involving unset variables, Docker daemon availability, invalid API tokens, Compose-version compatibility, and container network connectivity. The guide characterizes SMTP as suitable for simpler requirements and the API as a better option for stronger security features and higher email volumes.

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