You need to provide these variables
WORDPRESS_SMTP_HOST
- SMTP hostWORDPRESS_SMTP_PORT
- SMTP portWORDPRESS_SMTP_USERNAME
- SMTP usernameWORDPRESS_SMTP_PASSWORD
- SMTP passwordWORDPRESS_SMTP_FROM
- address from which emails are sent in wordpressWORDPRESS_SMTP_FROM_NAME
- name in wordpress emails
I'm using this with mailgun credentials and works great