Mail related error messages flooding the log every 75 minutes

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Sorry to hear you’re facing problems. :slightly_frowning_face:

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The Basics

  • Nextcloud Server version (e.g., 29.x.x):
    • Nextcloud Hub 25 Autumn (32.0.3)
  • Operating system and version (e.g., Ubuntu 24.04):
    • Linux
  • Web server and version (e.g, Apache 2.4.25):
    • Apache
  • PHP version (e.g, 8.3):
    • v8.4.12-nmm1
  • Is this the first time you’ve seen this error? (Yes / No):
    • Yes
  • When did this problem seem to first start?
    • Yesterday
  • Are you using CloudfIare, mod_security, or similar? (Yes / No)
    • No

Summary of the issue you are facing:

Since yesterday, my log is “flooded” with the following error messages every 75 minutes:

[core] Fehler: Error while running background job OCA\Mail\BackgroundJob\PreviewEnhancementProcessingJob (id: 30495, arguments: {“accountId”:3})

[PHP] Warnung: iconv(): Wrong encoding, conversion from “true” to “UTF-8” is not allowed at /www/htdocs/xxxxxxxx/klein-aber-fein.de/cloud/apps/mail/lib/IMAP/Charset/Converter.php#43

Steps to replicate it (hint: details matter!):

  1. Just looking in the log.

Log entries

Nextcloud

Please provide the log entries from your Nextcloud log that are generated during the time of problem (via the Copy raw option from Administration settings->Logging screen or from your nextcloud.log located in your data directory). Feel free to use a pastebin/gist service if necessary.

{"reqId":"AW8QTMR7r7ERWO7wAjIE","level":3,"time":"2026-01-07T07:05:01+00:00","remoteAddr":"","user":"--","app":"core","method":"","url":"--","message":"Error while running background job OCA\\Mail\\BackgroundJob\\PreviewEnhancementProcessingJob (id: 30495, arguments: {\"accountId\":3})","userAgent":"--","version":"32.0.3.2","exception":{"Exception":"ValueError","Message":"mb_convert_encoding(): Argument #3 ($from_encoding) contains invalid encoding \"true\"","Code":0,"Trace":[{"file":"/www/htdocs/xxxxxxxx/klein-aber-fein.de/cloud/apps/mail/lib/IMAP/Charset/Converter.php","line":62,"function":"mb_convert_encoding","args":[null,"UTF-8","true"]},{"file":"/www/htdocs/xxxxxxx/klein-aber-fein.de/cloud/apps/mail/lib/IMAP/MessageMapper.php","line":974,"function":"convert","class":"OCA\\Mail\\IMAP\\Charset\\Converter","type":"->","args":[{"__class__":"Horde_Mime_Part","parent":null}]},{"file":"/www/htdocs/xxxxxxxx/klein-aber-fein.de/cloud/apps/mail/lib/IMAP/MessageMapper.php","line":981,"function":"{closure:{closure:OCA\\Mail\\IMAP\\MessageMapper::getBodyStructureData():892}:951}","class":"OCA\\Mail\\IMAP\\MessageMapper","type":"->","args":["*** sensitive parameters replaced ***"]},{"function":"{closure:OCA\\Mail\\IMAP\\MessageMapper::getBodyStructureData():892}","class":"OCA\\Mail\\IMAP\\MessageMapper","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/www/htdocs/xxxxxxxx/klein-aber-fein.de/cloud/apps/mail/lib/IMAP/MessageMapper.php","line":892,"function":"array_map","args":[{"__class__":"Closure"},["*** sensitive parameters replaced ***","*** sensitive parameters replaced ***","*** sensitive parameters replaced ***","*** sensitive parameters replaced ***","*** sensitive parameters replaced ***","And 36 more entries, set log level to debug to see all entries"]]},{"file":"/www/htdocs/xxxxxxxx/klein-aber-fein.de/cloud/apps/mail/lib/IMAP/PreviewEnhancer.php","line":92,"function":"getBodyStructureData","class":"OCA\\Mail\\IMAP\\MessageMapper","type":"->","args":[{"__class__":"OCA\\Mail\\IMAP\\HordeImapClient","cacheFields":["HICenv","HICflags","HIChdrs","HICdate","HICsize","And 1 more entries, set log level to debug to see all entries"],"changed":true,"statuscache":true},"INBOX",[416,417,418,429,430,"And 36 more entries, set log level to debug to see all entries"],"asthomax@klein-aber-fein.de"]},{"file":"/www/htdocs/xxxxxxxx/klein-aber-fein.de/cloud/apps/mail/lib/Service/PreprocessingService.php","line":59,"function":"process","class":"OCA\\Mail\\IMAP\\PreviewEnhancer","type":"->","args":[{"__class__":"OCA\\Mail\\Account"},{"__class__":"OCA\\Mail\\Db\\Mailbox","id":20},[{"__class__":"OCA\\Mail\\Db\\Message","id":99501},{"__class__":"OCA\\Mail\\Db\\Message","id":99502},{"__class__":"OCA\\Mail\\Db\\Message","id":99503},{"__class__":"OCA\\Mail\\Db\\Message","id":99507},{"__class__":"OCA\\Mail\\Db\\Message","id":99510},"And 36 more entries, set log level to debug to see all entries"]]},{"file":"/www/htdocs/xxxxxxxx/klein-aber-fein.de/cloud/apps/mail/lib/BackgroundJob/PreviewEnhancementProcessingJob.php","line":77,"function":"process","class":"OCA\\Mail\\Service\\PreprocessingService","type":"->","args":[1766559901,{"__class__":"OCA\\Mail\\Account"}]},{"file":"/www/htdocs/xxxxxxxxx/klein-aber-fein.de/cloud/lib/public/BackgroundJob/Job.php","line":61,"function":"run","class":"OCA\\Mail\\BackgroundJob\\PreviewEnhancementProcessingJob","type":"->","args":[{"accountId":3}]},{"file":"/www/htdocs/xxxxxxxx/klein-aber-fein.de/cloud/lib/public/BackgroundJob/TimedJob.php","line":97,"function":"start","class":"OCP\\BackgroundJob\\Job","type":"->","args":[{"__class__":"OC\\BackgroundJob\\JobList"}]},{"file":"/www/htdocs/xxxxxxxxx/klein-aber-fein.de/cloud/lib/public/BackgroundJob/TimedJob.php","line":84,"function":"start","class":"OCP\\BackgroundJob\\TimedJob","type":"->","args":[{"__class__":"OC\\BackgroundJob\\JobList"}]},{"file":"/www/htdocs/xxxxxxxxx/klein-aber-fein.de/cloud/cron.php","line":175,"function":"execute","class":"OCP\\BackgroundJob\\TimedJob","type":"->","args":[{"__class__":"OC\\BackgroundJob\\JobList"}]}],"File":"/www/htdocs/xxxxxxxxx/klein-aber-fein.de/cloud/apps/mail/lib/IMAP/Charset/Converter.php","Line":62,"message":"Error while running background job OCA\\Mail\\BackgroundJob\\PreviewEnhancementProcessingJob (id: 30495, arguments: {\"accountId\":3})","exception":[],"CustomMessage":"Error while running background job OCA\\Mail\\BackgroundJob\\PreviewEnhancementProcessingJob (id: 30495, arguments: {\"accountId\":3})"},"id":"695e145455ef0"}

{"reqId":"AW8QTMR7r7ERWO7wAjIE","level":2,"time":"2026-01-07T07:05:01+00:00","remoteAddr":"","user":"--","app":"PHP","method":"","url":"--","message":"iconv(): Wrong encoding, conversion from \"true\" to \"UTF-8\" is not allowed at /www/htdocs/xxxxxxxx/klein-aber-fein.de/cloud/apps/mail/lib/IMAP/Charset/Converter.php#43","userAgent":"--","version":"32.0.3.2","data":{"app":"PHP"},"id":"695e145455ef5"}

Configuration

Nextcloud

The output of occ config:list system or similar is best, but, if not possible, the contents of your config.php file from /path/to/nextcloud is fine (make sure to remove any identifiable information!):

{

"system": {

    "instanceid": "\*\*\*REMOVED SENSITIVE VALUE\*\*\*",

    "passwordsalt": "\*\*\*REMOVED SENSITIVE VALUE\*\*\*",

    "secret": "\*\*\*REMOVED SENSITIVE VALUE\*\*\*",

    "trusted_domains": \[

        "klein-aber-fein.de",

        "www.klein-aber-fein.de"

    \],

    "datadirectory": "\*\*\*REMOVED SENSITIVE VALUE\*\*\*",

    "dbtype": "mysql",

    "version": "32.0.3.2",

    "overwrite.cli.url": "http:\\/\\/klein-aber-fein.de\\/cloud",

    "dbname": "\*\*\*REMOVED SENSITIVE VALUE\*\*\*",

    "dbhost": "\*\*\*REMOVED SENSITIVE VALUE\*\*\*",

    "dbport": "",

    "dbtableprefix": "BGsD4\_",

    "mysql.utf8mb4": true,

    "dbuser": "\*\*\*REMOVED SENSITIVE VALUE\*\*\*",

    "dbpassword": "\*\*\*REMOVED SENSITIVE VALUE\*\*\*",

    "installed": true,

    "tempdirectory": "\\/www\\/htdocs\\/w017f395\\/klein-aber-fein.de\\/cloud\\/tmp\\/",

    "mail_smtpmode": "smtp",

    "mail_sendmailmode": "pipe",

    "mail_from_address": "\*\*\*REMOVED SENSITIVE VALUE\*\*\*",

    "mail_domain": "\*\*\*REMOVED SENSITIVE VALUE\*\*\*",

    "maintenance": false,

    "theme": "",

    "loglevel": 2,

    "app_install_overwrite": {

        "0": "dashboardcharts",

        "1": "files_rightclick",

        "2": "occweb",

        "4": "passwords"

    },

    "updater.release.channel": "stable",

    "default_phone_region": "DE",

    "mail_smtphost": "\*\*\*REMOVED SENSITIVE VALUE\*\*\*",

    "mail_smtpport": "25",

    "mail_smtpauth": true,

    "mail_smtpname": "\*\*\*REMOVED SENSITIVE VALUE\*\*\*",

    "mail_smtppassword": "\*\*\*REMOVED SENSITIVE VALUE\*\*\*",

    "memories.db.triggers.fcu": true

}

}

Apps

Enabled:

  • bruteforcesettings: 5.0.0-dev.0

  • calendar: 6.1.3

  • cloud_federation_api: 1.16.0

  • comments: 1.22.0

  • contacts: 8.2.0

  • dav: 1.34.2

  • federatedfilesharing: 1.22.0

  • federation: 1.22.0

  • files: 2.4.0

  • files_downloadlimit: 5.0.0-dev.0

  • files_pdfviewer: 5.0.0-dev.0

  • files_reminders: 1.5.0

  • files_sharing: 1.24.1

  • files_trashbin: 1.22.0

  • files_versions: 1.25.0

  • firstrunwizard: 5.0.0-dev.0

  • gpxpod: 7.2.4

  • logcleaner: 1.2.3

  • logreader: 5.0.0-dev.0

  • lookup_server_connector: 1.20.0

  • mail: 5.6.5

  • music: 2.5.1

  • news: 27.2.0

  • nextcloud_announcements: 4.0.0-dev.0

  • notes: 4.12.4

  • notifications: 5.0.0-dev.0

  • oauth2: 1.20.0

  • password_policy: 4.0.0-dev.0

  • passwords: 2025.12.21

  • privacy: 4.0.0-dev.0

  • profile: 1.1.0

  • provisioning_api: 1.22.0

  • related_resources: 3.0.0-dev.0

  • serverinfo: 4.0.0-dev.0

  • settings: 1.15.1

  • sharebymail: 1.22.0

  • support: 4.0.0-dev.0

  • survey_client: 4.0.0-dev.0

  • systemtags: 1.22.0

  • tasks: 0.17.1

  • text: 6.0.1

  • theming: 2.7.0

  • theming_customcss: 1.19.0

  • twofactor_backupcodes: 1.21.0

  • updatenotification: 1.22.0

  • viewer: 5.0.0-dev.0

  • webhook_listeners: 1.3.0

  • workflowengine: 2.14.0

Disabled:

  • activity: 5.0.0-dev.0 (installed 5.0.0-dev.0)

  • admin_audit: 1.22.0

  • app_api: 32.0.0 (installed 32.0.0)

  • circles: 32.0.0 (installed 30.0.0)

  • contactsinteraction: 1.13.1 (installed 1.13.1)

  • cospend: 3.2.0 (installed 3.2.0)

  • dashboard: 7.12.0 (installed 7.11.0)

  • deck: 1.16.3 (installed 1.16.3)

  • encryption: 2.20.0

  • files_external: 1.24.0

  • files_rightclick: 0.15.1 (installed 0.15.1)

  • forms: 5.2.3 (installed 5.2.3)

  • hitobitologin: 1.1.1 (installed 1.1.1)

  • photos: 5.0.0-dev.1 (installed 4.0.0)

  • polls: 8.6.2 (installed 8.6.2)

  • recommendations: 5.0.0-dev.0 (installed 5.0.0-dev.0)

  • suspicious_login: 10.0.0-dev.0

  • twofactor_nextcloud_notification: 6.0.0-dev.0

  • twofactor_totp: 14.0.0

  • user_ldap: 1.23.0

  • user_status: 1.12.0 (installed 1.11.0)

  • weather_status: 1.12.0 (installed 1.11.0)

Tips for increasing the likelihood of a response

  • Use the preformatted text formatting option in the editor for all log entries and configuration output.
  • If screenshots are useful, feel free to include them.
    • If possible, also include key error output in text form so it can be searched for.
  • Try to edit log output only minimally (if at all) so that it can be ran through analyzers / formatters by those trying to help you.