After updating from OTRS 5 to OTRS 6 we can't login.

The login button ist not responding. 

here some lines from the Errorlog:

ERROR: OTRS-otrs.Console.pl-Maint::Email::MailQueue-11 Perl: 5.22.1 OS: linux Time: Mon Jan  8 16:52:02 2018

Message: CommunicationLog(ID:312,AccountType:-,AccountID:-,Direction:Outgoing,Transport:Email,ObjectLogType:Message,ObjectLogID:608)::Kernel::System::MailQueue => Permanent sending problem or we reached the sending attempt limit. Message will be removed

Traceback (1511): 

   Module: Kernel::System::CommunicationLog::_LogError Line: 538

   Module: Kernel::System::CommunicationLog::ObjectLog Line: 306

   Module: Kernel::System::MailQueue::_SendError Line: 853

   Module: Kernel::System::MailQueue::Send Line: 689

   Module: Kernel::System::Console::Command::Maint::Email::MailQueue::Send Line: 194

   Module: Kernel::System::Console::Command::Maint::Email::MailQueue::Run Line: 143

   Module: (eval) Line: 460

   Module: Kernel::System::Console::BaseCommand::Execute Line: 454

   Module: (eval) Line: 144

   Module: Kernel::System::Daemon::DaemonModules::SchedulerTaskWorker::Cron::Run Line: 123

   Module: Kernel::System::Daemon::DaemonModules::SchedulerTaskWorker::Run Line: 235

   Module: (eval) Line: 316

   Module: main::Start Line: 316

   Module: /opt/otrs//bin/otrs.Daemon.pl Line: 137

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