Redmine

About your application's environment
Ruby version              1.9.3 (x86_64-linux)
RubyGems version          1.8.23
Rack version              1.4
Rails version             3.2.6
Active Record version     3.2.6
Action Pack version       3.2.6
Active Resource version   3.2.6
Action Mailer version     3.2.6
Active Support version    3.2.6
Middleware                Rack::Cache, ActionDispatch::Static, Rack::Lock, #<ActiveSupport::Cache::Strategy::LocalCache::Middleware:0x00000002bd7160>, Rack::Runtime, Rack::MethodOverride, ActionDispatch::RequestId, Rails::Rack::Logger, ActionDispatch::ShowExceptions, ActionDispatch::DebugExceptions, ActionDispatch::RemoteIp, ActionDispatch::Callbacks, ActiveRecord::ConnectionAdapters::ConnectionManagement, ActiveRecord::QueryCache, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, ActionDispatch::ParamsParser, ActionDispatch::Head, Rack::ConditionalGet, Rack::ETag, ActionDispatch::BestStandardsSupport, OpenIdAuthentication
Application root          /opt/redmine
Environment               production
Database adapter          mysql2
Database schema version   20120731164049

I checked out redmine from github, and just on master branch.
use gmail's smtp service(port 587) and enabled the startles. No tis setting.

If I turned the setting to just :smtp, all mails send well. But for :async_smtp, no email would be send.
And no error tip, no error log. wired....

by the way, I use Unicorn as the server, and I found a warning log with in unicorn.log. I'm not sure whether it is related.

/opt/Ruby-1.9.3-p194/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/dependencies.rb:251:in `block in require': iconv will be deprecated in the future, use String#encode instead.