root@a47d817b-fd94-42e1-9a01-4986c9952996:/app/data/public/config# printenv | grep MAIL_SMTP_SERVER
CLOUDRON_MAIL_SMTP_SERVER=mail

So I assume the correct way to use these variables is:

getenv('CLOUDRON_MAIL_SMTP_SERVER')

Second:

I want to use the phpmailer addon for a Friendica instance. This addon replaces the mail() function with the PHPMailer library. The addon is configured and activated within the application but it still seems to look out for sendmail.

www-data@900e2935-6f37-42bc-8609-86876b5a2105:~/public/addon/phpmailer$ composer show -i
phpmailer/phpmailer v6.2.0 PHPMailer is a full-featured email creation and transfer class for PHP

LAMP log

sh: 1: /usr/sbin/sendmail: not found
sh: 1: /usr/sbin/sendmail: not found

Application log:

index [ERROR]: PHPMailer error {"email":{"fromName":"\"der Administrator von Friendica Social Network\"","fromAddress":"REMOVED","replyTo":"REMOVED","toAddress":"REMOVED","subject":"ttes","msgHtml":"teswdfrsdf","msgText":"teswdfrsdf","additionalMailHeader":[],"toUid":null},"ErrorInfo":"Could not instantiate mail function.","exception":{}} - {"file":"phpmailer.php","line":108,"function":"phpmailer_emailer_send_prepare","uid":"f4936f","process_id":26}

I also tried to use real (plain text) SMTP credentials with the same result The relevant part of my addon.config.php looks like this:

'phpmailer' => [
    // smtp (Boolean)
    // Enables SMTP relaying for outbound emails
    'smtp' => true,

    // smtp_server (String)
    // SMTP server host name
    'smtp_server' => getenv('CLOUDRON_MAIL_SMTP_SERVER'),

    // smtp_port (Integer)
    // SMTP server port number
    'smtp_port' => getenv('CLOUDRON_MAIL_SMTP_PORT'),

    // smtp_secure (String)
    // What kind of encryption to use on the SMTP connection.
    // Options: '', 'ssl' or 'tls'.
    'smtp_secure' => '',

    // smtp_port_s (Integer)
    // Secure SMTP server port number
    'smtp_port_s' => getenv('CLOUDRON_MAIL_SMTPS_PORT'),

    // smtp_username (String)
    // SMTP server authentication user name
    // Empty string disables authentication
    'smtp_username' => getenv('CLOUDRON_MAIL_SMTP_USERNAME'),

    // smtp_password (String)
    // SMTP server authentication password
    // Empty string disables authentication
    'smtp_password' => getenv('CLOUDRON_MAIL_SMTP_PASSWORD'),

    // smtp_from (String)
    // From address used when using the SMTP server
    // Example: no-reply@example.com
    'smtp_from' => getenv('CLOUDRON_MAIL_FROM'),
],