Redmine

Hello!
Redmine version 3.4.4.stable
Ruby version 2.3.6-p384 (2017-12-14) [x86_64-linux]
Rails version 4.2.8
Environment production
Database adapter Mysql2
SCM:
Subversion 1.7.14
Git 1.8.3.1
Filesystem
I have proxy and firewall before my redmine server. 993 is opens for outbond.
I am following the documentation at http://www.redmine.org/wiki/redmine/RedmineReceivingEmails with the "Fetching emails from an IMAP server" option.
I am tried the command:
sudo -E /usr/local/bin/rake --trace /var/www/redmine/Rakefile redmine:email:receive_imap RAILS_ENV="production" host=imap.gmail.com ssl=1 port=993 username=MYYYYAKKKKK@gmail.com password=MYYYYPAAAASS project=test status=assigned
It good worked only one-two times.
If I will try to do it after ~2-3 min I will have error:
rake aborted!
Errno::ENETUNREACH: Network is unreachable - connect(2) for "imap.gmail.com" port 993
/usr/local/lib/ruby/2.3.0/net/imap.rb:1082:in `initialize'
/usr/local/lib/ruby/2.3.0/net/imap.rb:1082:in `open'
/usr/local/lib/ruby/2.3.0/net/imap.rb:1082:in `initialize'
/opt/redmine/lib/redmine/imap.rb:30:in `new'
/opt/redmine/lib/redmine/imap.rb:30:in `check'
/opt/redmine/lib/tasks/email.rake:117:in `block (4 levels) in <top (required)>'
/opt/redmine/app/models/mailer.rb:433:in `with_synched_deliveries'
/opt/redmine/lib/tasks/email.rake:116:in `block (3 levels) in <top (required)>'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/task.rb:251:in `block in execute'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/task.rb:251:in `each'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/task.rb:251:in `execute'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/task.rb:195:in `block in invoke_with_call_chain'
/usr/local/lib/ruby/2.3.0/monitor.rb:214:in `mon_synchronize'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/task.rb:188:in `invoke_with_call_chain'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/task.rb:181:in `invoke'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/application.rb:160:in `invoke_task'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/application.rb:116:in `block (2 levels) in top_level'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/application.rb:116:in `each'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/application.rb:116:in `block in top_level'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/application.rb:125:in `run_with_threads'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/application.rb:110:in `top_level'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/application.rb:83:in `block in run'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/application.rb:186:in `standard_exception_handling'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/lib/rake/application.rb:80:in `run'
/usr/local/lib/ruby/gems/2.3.0/gems/rake-12.3.0/exe/rake:27:in `<top (required)>'
/usr/local/bin/rake:23:in `load'
/usr/local/bin/rake:23:in `<main>'
Tasks: TOP => redmine:email:receive_imap
What's it? How to solved it?