XF 2.2 Email to user failed: Expected response code 250 but got code 421 Service not available, closing transmission channel. Swiftmailer.

[MaximilianKohler]

I don't see any other threads covering this error.

It looks like something went wrong during the user registration, but I looked up the email and their user state is "valid".

Swift_TransportException: Email to xyz@gmail.com from forum@myforum.com failed: Expected response code 250 but got code "421", with message "421 Service not available, closing transmission channel. " src/vendor/swiftmailer/swiftmailer/lib/classes/Swift/Transport/AbstractSmtpTransport.php:459
Generated by: Unknown account Mar 18, 2025 at 9:25 AM

Stack trace

#0 src/vendor/swiftmailer/swiftmailer/lib/classes/Swift/Transport/AbstractSmtpTransport.php(344): Swift_Transport_AbstractSmtpTransport->assertResponseCode('421 Service not...', Array)
#1 src/vendor/swiftmailer/swiftmailer/lib/classes/Swift/Transport/EsmtpTransport.php(305): Swift_Transport_AbstractSmtpTransport->executeCommand('
.
', Array, Array, false, NULL)
#2 src/vendor/swiftmailer/swiftmailer/lib/classes/Swift/Transport/AbstractSmtpTransport.php(406): Swift_Transport_EsmtpTransport->executeCommand('
.
', Array)
#3 src/vendor/swiftmailer/swiftmailer/lib/classes/Swift/Transport/AbstractSmtpTransport.php(502): Swift_Transport_AbstractSmtpTransport->streamMessage(Object(Swift_Message))
#4 src/vendor/swiftmailer/swiftmailer/lib/classes/Swift/Transport/AbstractSmtpTransport.php(517): Swift_Transport_AbstractSmtpTransport->doMailTransaction(Object(Swift_Message), 'forum+c05491ae+...', Array, Array)
#5 src/vendor/swiftmailer/swiftmailer/lib/classes/Swift/Transport/AbstractSmtpTransport.php(206): Swift_Transport_AbstractSmtpTransport->sendTo(Object(Swift_Message), 'forum+c05491ae+...', Array, Array)
#6 src/XF/Mail/Mailer.php(315): Swift_Transport_AbstractSmtpTransport->send(Object(Swift_Message), Array)
#7 src/XF/Mail/Mail.php(579): XF\Mail\Mailer->send(Object(Swift_Message), Object(XF\Mail\SmtpTransport), NULL, true)
#8 src/XF/Service/User/AbstractConfirmationService.php(85): XF\Mail\Mail->send()
#9 src/XF/Service/User/AbstractConfirmationService.php(63): XF\Service\User\AbstractConfirmationService->sendConfirmationEmail()
#10 src/XF/Service/User/Registration.php(403): XF\Service\User\AbstractConfirmationService->triggerConfirmation()
#11 src/XF/Service/User/Registration.php(325): XF\Service\User\Registration->sendRegistrationContact()
#12 src/XF/Service/ValidateAndSavableTrait.php(42): XF\Service\User\Registration->_save()
#13 src/XF/Pub/Controller/Register.php(429): XF\Service\User\Registration->save()
#14 src/XF/Mvc/Dispatcher.php(352): XF\Pub\Controller\Register->actionRegister(Object(XF\Mvc\ParameterBag))
#15 src/XF/Mvc/Dispatcher.php(258): XF\Mvc\Dispatcher->dispatchClass('XF:Register', 'Register', Object(XF\Mvc\RouteMatch), Object(XF\Pub\Controller\Register), NULL)
#16 src/XF/Mvc/Dispatcher.php(115): XF\Mvc\Dispatcher->dispatchFromMatch(Object(XF\Mvc\RouteMatch), Object(XF\Pub\Controller\Register), NULL)
#17 src/XF/Mvc/Dispatcher.php(57): XF\Mvc\Dispatcher->dispatchLoop(Object(XF\Mvc\RouteMatch))
#18 src/XF/App.php(2513): XF\Mvc\Dispatcher->run()
#19 src/XF.php(524): XF\App->run()
#20 index.php(20): XF::runApp('XF\\Pub\\App')
#21 {main}

Request state

array(4) {
  ["url"] => string(18) "/register/register"
  ["referrer"] => string(44) "https://forum.mydomain.com/register/"
  ["_GET"] => array(1) {
    ["/register/register"] => string(0) ""
  }
  ["_POST"] => array(15) {
    ["_xfToken"] => string(8) "********"
    ["username"] => string(0) ""
    ["snip"] => string(8) "username-probably"
    ["snip"] => string(0) ""
    ["snip"] => string(21) "xyz@gmail.com"
    ["email"] => string(0) ""
    ["snip"] => string(8) "********"
    ["g-recaptcha-response"] => string(2915) "huge-string"
    ["h-captcha-response"] => string(2915) "huge-string"
    ["accept"] => string(1) "1"
    ["reg_key"] => string(16) "snip"
    ["snip"] => string(16) "America/New_York"
    ["_xfRequestUri"] => string(10) "/register/"
    ["_xfWithData"] => string(1) "1"
    ["_xfResponseType"] => string(4) "json"
  }
}