Nextcloud Calendar does not send e-mails

Nextcloud version : 24.0.6
Operating system and version (eg, Ubuntu 20.04): Official Nextcloud docker image (24.0.6)
Apache or nginx version : Apache included with Official Nextcloud docker image (24.0.6)
PHP version (eg, 7.4): PHP included with Official Nextcloud docker image (24.0.6)

Nextcloud calendar does not send any emails.

I’ve only recently started using the calendar. When creating new events, e-mail invites are not sent - neither to other Nextcloud users nor to “external” email recipients. Changes to calendar events also do not cause emails to be sent. Lastly, email reminders for events are also not sent.

The email server is correctly set up in Settings → Basic settings, and sending test emails work. I use “” as Nextcloud’s (from:) email address; nothing special there either.

I’ve also verified the cron job to run; it runs reliably every 30 seconds and does not report any errors.

My nextcloud set-up uses my own mail server; when I test nextcloud’s email server settings I can see nextcloud connecting and sending successfully in my SMPT server logs. However, when creating or modifyinc calendar invites, Nextcloud never connects to the SMTP server.

Steps to replicate it:

  1. Run Nextcloud 24.0.6 from dockerhub
  2. Create a calendar invite with guests; save the invite.
  3. No email is being sent. Check SMTP server logs - Nextcloud did not connect.
  4. Go to Settings → Basic, “Email server” section. Press “Send email” button. An email is being sent. SMTP server logs show Nextcloud connecting and sending the email.

The output of your Nextcloud log in Admin > Logging:

That log is empty.

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

$CONFIG = array (
  'instanceid' => 'XXXXXXXXX',
  'overwrite.cli.url' => '',
  'overwriteprotocol' => 'https',
  'overwritehost' => '',
  'trusted_proxies' =>
  array (
    0 => '*',
  'trusted_domains' =>
  array (
    0 => '',
  'datadirectory' => '/var/www/html/data',
  'dbtype' => 'mysql',
  'version' => '',
  'integrity.check.disabled' => true,
  'default_language' => 'de',
  'default_locale' => 'de',
  'trashbin_retention_obligation' => 'auto, 30',
  'version_retention_obligation' => 'auto, 30',
  'memcache.local' => '\\OC\\Memcache\\APCu',
  'log_type' => 'errorlog',
  'loglevel' => 2,
  'dbname' => 'XXXXXXXXX',
  'dbhost' => 'mariadb',
  'dbport' => '',
  'dbtableprefix' => 'XXXXX',
  'mysql.utf8mb4' => true,
  'dbuser' => 'XXXXXXXXX',
  'dbpassword' => 'XXXXXXXXX',
  'installed' => true,
  'mail_smtpmode' => 'smtp',
  'mail_smtpsecure' => 'ssl',
  'mail_sendmailmode' => 'smtp',
  'mail_smtpauthtype' => 'LOGIN',
  'mail_from_address' => 'cloud',
  'mail_domain' => '',
  'mail_smtpauth' => 1,
  'mail_smtphost' => '',
  'mail_smtpport' => '465',
  'mail_smtpname' => 'XXXXXXXXX',
  'mail_smtppassword' => 'XXXXXXXXX',
  'maintenance' => false,
  'theme' => '',
  '' => 'stable',
  'app_install_overwrite' =>
  array (
    0 => 'epubreader',

The output of your Apache/nginx/system log in /var/log/____:

N/A as this is an SMTP client issue.

Output errors in nextcloud.log in /var/www/ or as admin user in top right menu, filtering for errors. Use a pastebin service if necessary.

No errors.

Not sure, if this is the same problem, but with the latest Nextcloud version neither Evolution nor Korganizer are able to send invitation emails, when using the Nexcloud CalDAV backend.
In both applications when creating an invitation and adding an email address, it is converted to something like
which obviously isn’t a valid email address. Therefore no email is sent.

Issue continues to exist in Calendar 3.5.1.

You may report the issue in the bug-tracker:

if it does not exist.