Redmine

Environment:
Redmine version 4.1.1.stable
Ruby version 2.5.5-p157 (2019-03-15) [x86_64-linux]
Rails version 5.2.4.2
Environment production
Database adapter Mysql2
Mailer queue ActiveJob::QueueAdapters::AsyncAdapter
Mailer delivery smtp
SCM:
Git 2.17.1
Filesystem
Redmine plugins:
no plugin installed

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tab: email notifications -> send testmail -> An error occurred while sending mail (Net::ReadTimeout)

error log:
Started POST "/admin/test_email" for 193.197.148.126 at 2020-07-10 11:30:39 +0200
Processing by AdminController#test_email as HTML
Parameters: {"authenticity_token"=>"1Ha2Oei4QWq6qKfsmeidvtXvfn0GtzoVUiVQe/6V2oDidyYrK86ir2hZ5bSMiUHXwoVgDB2XdAWKWFLy2QIhtw=="}
Current user: hoessa (id=5)
Rendering mailer/test_email.text.erb within layouts/mailer
Rendered mailer/test_email.text.erb within layouts/mailer (0.1ms)

1. default configuration options for all environments
   default: # Outgoing emails configuration # See the examples below and the Rails guide for more configuration options: # http://guides.rubyonrails.org/action_mailer_basics.html#action-mailer-configuration # email_delivery:

1. ==== Simple SMTP server at localhost #
2. email_delivery:
3. delivery_method: :smtp
4. smtp_settings:
5. address: "is@lhxxx.de"
6. port: 465 #
7. ==== SMTP server at example.com using LOGIN authentication and checking HELO for foo.com #
   email_delivery:
   delivery_method: :smtp
   smtp_settings:
   address: "huhu.de"
   port: 465
   authentication: :login
   domain: "huhu.de"
   user_name: 'is@huhu.de'
   password: 'xxx' #
8. ==== SMTP server at example.com using PLAIN authentication

whats wrong?
THX for any tips!