The config file:
cd /usr/share/redmine/config
sudo cp configuration.yml.example /etc/redmine/default/ //可以放到default目录下，也可以直接放在当前目录，反正都能读到
sudo mv configuration.yml.example configuration.yml //重命名去掉.example后缀
sudo vim configuration.yml //里面有很多关于在各种环境下配置的 指导
比如：exchange邮箱（如果在同一个网域）
default: //默认，如果configuration.yml最下面的production有值，将覆盖default
# Outgoing emails configuration
email_delivery:
delivery_method: :smtp
smtp_settings:
address: cnmail.**.com
port: 25 //要注意哦，如果exchange邮箱和redmine在同一台电脑，或者在同一个网域，则，下面domain,authentication,user_name之类都不需要，都注释掉
//否则，会报 504 5.7.4 Unrecognized authentication type
比如：利用qq邮箱：
# Outgoing email settings //测试成功
production:
delivery_method: :smtp
smtp_settings:
address: smtp.qq.com
port: 25
domain: qq.com
authentication: :login
user_name: 91**8301@qq.com
password: ******* //填写自己的邮箱和密码，且该邮箱要和设置页的发送邮箱一致
Related links:
http://www.redmine.org/projects/redmine/wiki/HowTo_Install_Redmine_25x_on_Ubuntu_1404_with_Apache2_Phusion_Passenger_MySQL_and_Subversion //good
http://blog.csdn.net/pochuanpiao/article/details/12840985 //good
http://www.redmine.org/projects/redmine/wiki/EmailConfiguration //email configuration
http://www.aiezu.com/code/exchange2010_smtp_unrecognized_authentication_type.html //504 5.7.4 Unrecognized authentication type
http://xianghuaclm.blog.163.com/blog/static/66687832012046921370/