Increase visibility of e-mail delivery failures

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

When there is a configuration error or the mail server is unable to accept mails from nextcloud (e.g. due to fail2ban) there is no indication that nextcloud is not able to send emails in the nextcloud logging or in the warnings on admin page.

Steps to reproduce

1. Block the server's ip adress on which nextcloud is installed on your mail server
2. Try to send a mail through nextcloud (e.g. when sharing something to an email adress.
3. No email is sent, but there is no error to the user, in the logs or in the warnings on admin page.

Expected behavior

• The user should be notified that the mail to the recipient of the share could not be sent
• The fact that mails could not be sent should be logged in the Nextcloud log and displayed in the warnings on the admin page.

Installation method

Community Manual installation with Archive

Nextcloud Server version

27

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.1

Web server

Nginx

Database engine version

MariaDB

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

#./nextcloud_occ.sh config:list system
{
    "system": {
        "allow_local_remote_servers": true,
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "***REMOVED SENSITIVE VALUE***",
            "***REMOVED SENSITIVE VALUE***",
            "***REMOVED SENSITIVE VALUE***",
            "***REMOVED SENSITIVE VALUE***"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "overwrite.cli.url": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "27.1.3.2",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "default_phone_region": "DE",
        "enabledPreviewProviders": [
            "OC\\Preview\\PNG",
            "OC\\Preview\\JPEG",
            "OC\\Preview\\GIF",
            "OC\\Preview\\HEIC",
            "OC\\Preview\\SVG",
            "OC\\Preview\\BMP",
            "OC\\Preview\\XBitmap",
            "OC\\Preview\\MP3",
            "OC\\Preview\\TXT",
            "OC\\Preview\\MarkDown"
        ],
        "installed": true,
        "memcache.local": "\\OC\\Memcache\\Redis",
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": 6379
        },
        "filelocking.debug": true,
        "log_type": "file",
        "logtimezone": "Europe\/Berlin",
        "logfile": "***REMOVED SENSITIVE VALUE***\/nextcloud.log",
        "loglevel": 2,
        "mail_smtpmode": "smtp",
        "mail_smtpauthtype": "LOGIN",
        "mail_smtpauth": 1,
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "587",
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "trashbin_retention_obligation": "30, 30",
        "maintenance": false,
        "mysql.utf8mb4": true,
        "theme": "",
        "has_rebuilt_cache": true,
        "mail_sendmailmode": "smtp",
        "encryption.key_storage_migrated": false,
        "data-fingerprint": "e86a39fb84481ffab93dcfa51062cd95",
        "encryption.legacy_format_support": false,
        "app_install_overwrite": [
            "cookbook"
        ]
    }
}

List of activated Apps

Enabled:
  - activity: 2.19.0
  - calendar: 4.5.3
  - circles: 27.0.1
  - cloud_federation_api: 1.10.0
  - collectives: 2.8.2
  - comments: 1.17.0
  - contacts: 5.4.2
  - contactsinteraction: 1.8.0
  - cookbook: 0.10.2
  - dav: 1.27.0
  - deck: 1.11.0
  - encryption: 2.15.0
  - federatedfilesharing: 1.17.0
  - federation: 1.17.0
  - files: 1.22.0
  - files_external: 1.19.0
  - files_pdfviewer: 2.8.0
  - files_reminders: 1.0.0
  - files_rightclick: 1.6.0
  - files_sharing: 1.19.0
  - files_trashbin: 1.17.0
  - files_versions: 1.20.0
  - forms: 3.3.1
  - gpxpod: 5.0.13
  - logreader: 2.12.0
  - lookup_server_connector: 1.15.0
  - mail: 3.4.4
  - maps: 1.1.1
  - nextcloud_announcements: 1.16.0
  - notes: 4.8.1
  - notifications: 2.15.0
  - oauth2: 1.15.1
  - password_policy: 1.17.0
  - photos: 2.3.0
  - privacy: 1.11.0
  - provisioning_api: 1.17.0
  - recommendations: 1.6.0
  - related_resources: 1.2.0
  - richdocuments: 8.2.2
  - serverinfo: 1.17.0
  - settings: 1.9.0
  - sharebymail: 1.17.0
  - support: 1.10.0
  - survey_client: 1.15.0
  - systemtags: 1.17.0
  - tasks: 0.15.0
  - text: 3.8.0
  - theming: 2.2.0
  - twofactor_backupcodes: 1.16.0
  - twofactor_totp: 9.0.0
  - updatenotification: 1.17.0
  - user_status: 1.7.0
  - viewer: 2.1.0
  - workflowengine: 2.9.0
Disabled:
  - admin_audit: 1.17.0
  - bruteforcesettings: 2.7.0 (installed 2.0.1)
  - dashboard: 7.7.0 (installed 7.5.0)
  - firstrunwizard: 2.16.0 (installed 2.14.0)
  - suspicious_login: 5.0.0
  - user_ldap: 1.17.0
  - weather_status: 1.7.0 (installed 1.5.0)

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

No response

Additional info

No response

Start by reproducing the failed SMTP delivery described in the issue, using the sharebymail app and the configured mail settings. Trace how the failure is handled for a share-by-email action, then check the existing Nextcloud log and admin warnings behavior. Done means the user is notified, the failure is logged, and an admin warning is displayed.