Redmine

i cofigure the mail setting in "configuration.yml" as:

default: # Outgoing emails configuration (see examples above)
email_delivery:
delivery_method: :smtp
smtp_settings:
enable_starttls_auto: true
address: "smtp.gmail.com"
port: 587
domain: "smtp.gmail.com"
authentication: :plain
user_name: "mymail@gmail.com"
password: "mypassword"

when i click on the "send a test email" button in "email notification: field it shows an error :
_
An error occurred while sending mail (execution expired)

any suggestion or solution

i am using :-

Redmine version                          2.3.1.stable
  Ruby version                             1.9.3 (i686-linux)
  Rails version                            3.2.13
  Environment                              production
  Database adapter                         Mysql2

thank you