Linuxserver docker piwigo won't send mail

I had a piwigo site, running in a LXC. After a complete disk crash, I installed the latest docker Piwigo version.

Here’s my docker-compose.yml file:
version: 2
services:

  • piwidb:*

  • image: mariadb:10*

  • container_name: piwigo_mariadb*

  • restart: unless-stopped*

  • environment:*

  •  MYSQL_ROOT_PASSWORD: 'YYYYYYYYYYYYYYYY'*
    
  •  MYSQL_DATABASE: 'piwigo_db'*
    
  •  MYSQL_USER: 'piwigo_user'*
    
  •  MYSQL_PASSWORD: 'XXXXXXXXXXXXXXXXX'*
    
  • volumes: *

  •  - piwigo_db:/var/lib/mysql*
    
  • piwigo:*

  • image: linuxserver/piwigo*

  • container_name: piwigo*

  • environment:*

  •  - PUID=1000*
    
  •  - PGID=1000*
    
  •  - TZ=Europe/Paris*
    
  • volumes:*

  •  - piwigo_data:/config*
    
  • ports:*

  •  - 8087:80*
    
  • restart: unless-stopped*

  • links:*

  •  - piwidb*
    

I tried to send emails from my piwigo site. I use mailgun as mailrelay

My docker config, running on debian buster:
Client: Docker Engine - Community

  • Version: 19.03.4*
  • API version: 1.40*
  • Go version: go1.12.10*
  • Git commit: 9013bf583a*
  • Built: Fri Oct 18 15:52:16 2019*
  • OS/Arch: linux/amd64*
  • Experimental: false*

Server: Docker Engine - Community

  • Engine:*
  • Version: 19.03.4*
  • API version: 1.40 (minimum version 1.12)*
  • Go version: go1.12.10*
  • Git commit: 9013bf583a*
  • Built: Fri Oct 18 15:50:48 2019*
  • OS/Arch: linux/amd64*
  • Experimental: false*
  • containerd:*
  • Version: 1.2.10*
  • GitCommit: b34a5c8af56e510852c35414db4c1f4fa6172339*
  • runc:*
  • Version: 1.0.0-rc8+dev*
  • GitCommit: 3e425f80a8c931f88e6d94a8c831b9d5aa481657*
  • docker-init:*
  • Version: 0.18.0*
  • GitCommit: fec3683*

I set up, and tried many parameters in the /config/www/gallery/local/config/config.inc.php
// ±----------------------------------------------------------------------+
// | email |
// ±----------------------------------------------------------------------+

// send_bcc_mail_webmaster: send bcc mail to webmaster. Set true for debug
// or test.
$conf['send_bcc_mail_webmaster'] = false;

// define the name of sender mail: if value is empty, gallery title is used
$conf['mail_sender_name'] = 'Piwigo 4 Ever';

// define the email of sender mail: if value is empty, webmaster email is used
$conf['mail_sender_email'] = 'user@mg.mydomain.tld';

// set true to allow text/html emails
$conf['mail_allow_html'] = true;

// smtp configuration (work if fsockopen function is allowed for smtp port)
// smtp_host: smtp server host
//  if null, regular mail function is used
//   format: hoststring[:port]
//   exemple: smtp.pwg.net:21
// smtp_user/smtp_password: user & password for smtp authentication
$conf['smtp_host'] = 'smtp.mailgun.org:465';
$conf['smtp_user'] = 'smtpuser@mg.domain.tld';
$conf['smtp_password'] = 'xxxxxxxxxxxx';

// 'ssl' or 'tls'
$conf['smtp_secure'] = 'tls';

I tried some Email sending, while user registrations, or with Piwecard plugin.
However, I can’t see any incoming connections, on mailgun.

My questions:

  • I was not able to find any useful log files. Where can I find log files logging SMTP attempts ? Where can I activate more verbose logs ?
  • Is the linuxserver docker Piwigo image able to send Emails ?
  • Any other useful tricks ?