Email is sent but stuck in Outbox too. about mail HOT 2 OPEN

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[mail] Error: Could not send message: Error when communicating with the server.
POST /index.php/apps/mail/api/outbox/38
from {ip} by {user} at May 2, 2024, 10:49:07 AM

{"reqId":"3lqDbXk4dO7BvfSHFpAa","level":3,"time":"2024-05-02T03:49:07+00:00","remoteAddr":"{ip}","user":"{user}","app":"mail","method":"POST","url":"/index.php/apps/mail/api/outbox/38","message":"Could not send message: Error when communicating with the server.","userAgent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36","version":"28.0.4.1","exception":{"Exception":"OCA\Mail\Exception\ServiceException","Message":"Could not send message: Error when communicating with the server.","Code":2,"Trace":[{"file":"/var/www/nextcloud/apps/mail/lib/Service/MailTransmission.php","line":343,"function":"sendMessage","class":"OCA\Mail\Service\MailTransmission","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Service/OutboxService.php","line":142,"function":"sendLocalMessage","class":"OCA\Mail\Service\MailTransmission","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Controller/OutboxController.php","line":247,"function":"sendMessage","class":"OCA\Mail\Service\OutboxService","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":230,"function":"send","class":"OCA\Mail\Controller\OutboxController","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":137,"function":"executeController","class":"OC\AppFramework\Http\Dispatcher","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/App.php","line":184,"function":"dispatch","class":"OC\AppFramework\Http\Dispatcher","type":"->"},{"file":"/var/www/nextcloud/lib/private/Route/Router.php","line":315,"function":"main","class":"OC\AppFramework\App","type":"::"},{"file":"/var/www/nextcloud/lib/base.php","line":1069,"function":"match","class":"OC\Route\Router","type":"->"},{"file":"/var/www/nextcloud/index.php","line":39,"function":"handleRequest","class":"OC","type":"::"}],"File":"/var/www/nextcloud/apps/mail/lib/Service/MailTransmission.php","Line":273,"Previous":{"Exception":"Horde_Mime_Exception","Message":"Error when communicating with the server.","Code":2,"Trace":[{"file":"/var/www/nextcloud/apps/mail/vendor/bytestream/horde-mime/lib/Horde/Mime/Mail.php","line":479,"function":"send","class":"Horde_Mime_Part","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Service/MailTransmission.php","line":271,"function":"send","class":"Horde_Mime_Mail","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Service/MailTransmission.php","line":343,"function":"sendMessage","class":"OCA\Mail\Service\MailTransmission","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Service/OutboxService.php","line":142,"function":"sendLocalMessage","class":"OCA\Mail\Service\MailTransmission","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Controller/OutboxController.php","line":247,"function":"sendMessage","class":"OCA\Mail\Service\OutboxService","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":230,"function":"send","class":"OCA\Mail\Controller\OutboxController","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":137,"function":"executeController","class":"OC\AppFramework\Http\Dispatcher","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/App.php","line":184,"function":"dispatch","class":"OC\AppFramework\Http\Dispatcher","type":"->"},{"file":"/var/www/nextcloud/lib/private/Route/Router.php","line":315,"function":"main","class":"OC\AppFramework\App","type":"::"},{"file":"/var/www/nextcloud/lib/base.php","line":1069,"function":"match","class":"OC\Route\Router","type":"->"},{"file":"/var/www/nextcloud/index.php","line":39,"function":"handleRequest","class":"OC","type":"::"}],"File":"/var/www/nextcloud/apps/mail/vendor/bytestream/horde-mime/lib/Horde/Mime/Part.php","Line":1642,"Previous":{"Exception":"Horde_Mail_Exception","Message":"Error when communicating with the server.","Code":2,"Trace":[{"file":"/var/www/nextcloud/apps/mail/vendor/bytestream/horde-mime/lib/Horde/Mime/Part.php","line":1620,"function":"send","class":"Horde_Mail_Transport_Smtphorde","type":"->"},{"file":"/var/www/nextcloud/apps/mail/vendor/bytestream/horde-mime/lib/Horde/Mime/Mail.php","line":479,"function":"send","class":"Horde_Mime_Part","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Service/MailTransmission.php","line":271,"function":"send","class":"Horde_Mime_Mail","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Service/MailTransmission.php","line":343,"function":"sendMessage","class":"OCA\Mail\Service\MailTransmission","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Service/OutboxService.php","line":142,"function":"sendLocalMessage","class":"OCA\Mail\Service\MailTransmission","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Controller/OutboxController.php","line":247,"function":"sendMessage","class":"OCA\Mail\Service\OutboxService","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":230,"function":"send","class":"OCA\Mail\Controller\OutboxController","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":137,"function":"executeController","class":"OC\AppFramework\Http\Dispatcher","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/App.php","line":184,"function":"dispatch","class":"OC\AppFramework\Http\Dispatcher","type":"->"},{"file":"/var/www/nextcloud/lib/private/Route/Router.php","line":315,"function":"main","class":"OC\AppFramework\App","type":"::"},{"file":"/var/www/nextcloud/lib/base.php","line":1069,"function":"match","class":"OC\Route\Router","type":"->"},{"file":"/var/www/nextcloud/index.php","line":39,"function":"handleRequest","class":"OC","type":"::"}],"File":"/var/www/nextcloud/apps/mail/vendor/bytestream/horde-mail/lib/Horde/Mail/Transport/Smtphorde.php","Line":145,"Previous":{"Exception":"Horde_Smtp_Exception","Message":"Error when communicating with the server.","Code":2,"Trace":[{"file":"/var/www/nextcloud/apps/mail/vendor/nextcloud/horde-smtp/lib/Horde/Smtp.php","line":1046,"function":"read","class":"Horde_Smtp_Connection","type":"->"},{"file":"/var/www/nextcloud/apps/mail/vendor/nextcloud/horde-smtp/lib/Horde/Smtp.php","line":1112,"function":"_getResponse","class":"Horde_Smtp","type":"->"},{"file":"/var/www/nextcloud/apps/mail/vendor/nextcloud/horde-smtp/lib/Horde/Smtp.php","line":757,"function":"_processData","class":"Horde_Smtp","type":"->"},{"file":"/var/www/nextcloud/apps/mail/vendor/bytestream/horde-mail/lib/Horde/Mail/Transport/Smtphorde.php","line":143,"function":"send","class":"Horde_Smtp","type":"->"},{"file":"/var/www/nextcloud/apps/mail/vendor/bytestream/horde-mime/lib/Horde/Mime/Part.php","line":1620,"function":"send","class":"Horde_Mail_Transport_Smtphorde","type":"->"},{"file":"/var/www/nextcloud/apps/mail/vendor/bytestream/horde-mime/lib/Horde/Mime/Mail.php","line":479,"function":"send","class":"Horde_Mime_Part","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Service/MailTransmission.php","line":271,"function":"send","class":"Horde_Mime_Mail","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Service/MailTransmission.php","line":343,"function":"sendMessage","class":"OCA\Mail\Service\MailTransmission","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Service/OutboxService.php","line":142,"function":"sendLocalMessage","class":"OCA\Mail\Service\MailTransmission","type":"->"},{"file":"/var/www/nextcloud/apps/mail/lib/Controller/OutboxController.php","line":247,"function":"sendMessage","class":"OCA\Mail\Service\OutboxService","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":230,"function":"send","class":"OCA\Mail\Controller\OutboxController","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":137,"function":"executeController","class":"OC\AppFramework\Http\Dispatcher","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/App.php","line":184,"function":"dispatch","class":"OC\AppFramework\Http\Dispatcher","type":"->"},{"file":"/var/www/nextcloud/lib/private/Route/Router.php","line":315,"function":"main","class":"OC\AppFramework\App","type":"::"},{"file":"/var/www/nextcloud/lib/base.php","line":1069,"function":"match","class":"OC\Route\Router","type":"->"},{"file":"/var/www/nextcloud/index.php","line":39,"function":"handleRequest","class":"OC","type":"::"}],"File":"/var/www/nextcloud/apps/mail/vendor/nextcloud/horde-smtp/lib/Horde/Smtp/Connection.php","Line":130}}},"message":"Could not send message: Error when communicating with the server.","exception":[],"CustomMessage":"Could not send message: Error when communicating with the server."},"id":"66330d3d4b9d9"}

from mail.

Duplicate of #8435.

A fix is coming with v3.7.

from mail.