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