SMTP: temporary failure in name resolution

I am trying to set up vaultwarden docker container. I got a sub domain with a lets encrypt certificate pointing to my vaultwarden instance. When trying to configure the SMTP Email Settings section in the admin panel, I am facing some issues with respect to sending a test email.

I am using the smtp server of my domain name provider. It uses port 465. I ticked “Force TLS” and unticked “Enable Secure SMTP”.
“From Address” is my email address
“From Name” left blank
Username and password

When I try to send a test mail, I get the following error message:


Nobody with the same error message??

Via the diagnostics tab, I just learned that my internet access and DNS check failed. So I guess, I need to change something in the way I created the docker container.

Here’s my config. Would be nice if somebody can push me into the right direction.

Your environment (Generated via diagnostics page)

  • Vaultwarden version: v1.23.1
  • Web-vault version: v2.25.0
  • Running within Docker: true (Base: Debian)
  • Environment settings overridden: true
  • Uses a reverse proxy: true
  • IP Header check: true (X-Real-IP)
  • Internet access: false
  • Internet access via a proxy: false
  • DNS Check: false
  • Time Check: true
  • Domain Configuration Check: true
  • HTTPS Check: true
  • Database type: SQLite
  • Database version: 3.35.4
  • Clients used:
  • Reverse proxy and version:
  • Other relevant information:

Config (Generated via diagnostics page)

Show Running Config

Environment settings which are overridden: ADMIN_TOKEN

  "_duo_akey": null,
  "_enable_duo": false,
  "_enable_email_2fa": false,
  "_enable_smtp": true,
  "_enable_yubico": true,
  "_ip_header_enabled": true,
  "admin_token": "***",
  "allowed_iframe_ancestors": "",
  "attachments_folder": "data/attachments",
  "authenticator_disable_time_drift": false,
  "data_folder": "data",
  "database_max_conns": 10,
  "database_url": "****/**.*******",
  "db_connection_retries": 15,
  "disable_2fa_remember": false,
  "disable_admin_token": false,
  "disable_icon_download": false,
  "domain": "*****://**.*************.**",
  "domain_origin": "*****://**.*************.**",
  "domain_path": "",
  "domain_set": true,
  "duo_host": null,
  "duo_ikey": null,
  "duo_skey": null,
  "email_attempts_limit": 3,
  "email_expiration_time": 600,
  "email_token_size": 6,
  "emergency_access_allowed": true,
  "emergency_notification_reminder_schedule": "0 5 * * * *",
  "emergency_request_timeout_schedule": "0 5 * * * *",
  "enable_db_wal": true,
  "extended_logging": true,
  "helo_name": null,
  "hibp_api_key": null,
  "icon_blacklist_non_global_ips": true,
  "icon_blacklist_regex": null,
  "icon_cache_folder": "data/icon_cache",
  "icon_cache_negttl": 259200,
  "icon_cache_ttl": 2592000,
  "icon_download_timeout": 10,
  "incomplete_2fa_schedule": "30 * * * * *",
  "incomplete_2fa_time_limit": 2,
  "invitation_org_name": "Vaultwarden Vester",
  "invitations_allowed": true,
  "ip_header": "X-Real-IP",
  "job_poll_interval_ms": 30000,
  "log_file": null,
  "log_level": "Info",
  "log_timestamp_format": "%Y-%m-%d %H:%M:%S.%3f",
  "org_attachment_limit": null,
  "org_creation_users": "*******@*************.**",
  "password_iterations": 100000,
  "reload_templates": false,
  "require_device_email": false,
  "rsa_key_filename": "data/rsa_key",
  "send_purge_schedule": "0 5 * * * *",
  "sends_allowed": true,
  "sends_folder": "data/sends",
  "show_password_hint": false,
  "signups_allowed": true,
  "signups_domains_whitelist": "",
  "signups_verify": true,
  "signups_verify_resend_limit": 6,
  "signups_verify_resend_time": 3600,
  "smtp_accept_invalid_certs": false,
  "smtp_accept_invalid_hostnames": false,
  "smtp_auth_mechanism": null,
  "smtp_debug": false,
  "smtp_explicit_tls": true,
  "smtp_from": "*******@*************.**",
  "smtp_from_name": "Vaultwarden",
  "smtp_host": "****.******.**",
  "smtp_password": "***",
  "smtp_port": 465,
  "smtp_ssl": false,
  "smtp_timeout": 15,
  "smtp_username": "*******@*************.**",
  "templates_folder": "data/templates",
  "trash_auto_delete_days": 90,
  "trash_purge_schedule": "0 5 0 * * *",
  "use_syslog": false,
  "user_attachment_limit": null,
  "web_vault_enabled": true,
  "web_vault_folder": "web-vault/",
  "websocket_address": "",
  "websocket_enabled": false,
  "websocket_port": 3012,
  "yubico_client_id": null,
  "yubico_secret_key": null,
  "yubico_server": null

I would suggest to set “smtp_debug” to true and try again, then check the Logfile to see if there are more detailed information

OK, I set smtp_debug to true. Then I try to send another test Email. In the container logs I found only the familiar error message:

[2022-01-24 20:07:02.394][request][INFO] POST /admin/test/smtp/

[2022-01-24 20:07:07.542][vaultwarden::mail][ERROR] SMTP Connection error: failed to lookup address information: Temporary failure in name resolution

[2022-01-24 20:07:07.544][response][INFO] POST /admin/test/smtp (test_smtp) => 400 Bad Request

As mentioned DNS resolution seems to be the cause of your SMTP issues.
It also seems that your Vaultwarden instance is unable to have further basic internet connectivity. I’m not too sure how Vaultwarden determines this, but it appears that DNS reaches out to GitHub.

I would try to see if you can ping an external IP such as (Google’s DNS servers) from either the host directly or use $ docker exec ... command to ping from inside the docker container to try and reach out to the greater internet.

If you are able to get to your Vaultwarden instance on your LAN, then I would venture to guess it’s a firewall rule issue somewhere on your set up.