SharePoint 2010 : Configure Outgoing e-mails on Windows Server 2008

First, Configure our Server "Windows Server 2008":

Install SMTP Server
- From Administrative tools -> Server Manager

- click Add Feature and select SMTP Server

 - you will need to add roles & features required for SMTP Server

- Wizard will continue the steps and finally, you will get this result

Configure IIS 7 & SMTP Email
- from Administrative tools -> Internet Information Services (IIS) Manager

 - double click SMTP E-mail

Enter E-mail Address for sender e-mail address
Deliver e-mail to SMTP server: to deliver e-mail messages immediately. This requires an operational SMTP server for which the user has credentials(SMTP Server, Port and credentials)

Run SMTP Service Automatically
      1.Click Start, point to Administrative Tools, and then click Services. 2.In Services, right-click Simple Mail Transfer Protocol (SMTP), and then select Properties. 3.In the Simple Mail Transfer Protocol (SMTP) Properties dialog box, on the General tab, in the Startup type list, select Automatic.

Second, Configure SharePoint 2010 from Central Administration or using STSADM
1- using STSADM:
stsadm -o email -outsmtpserver [server] -fromaddress [fromaddress] -replytoaddress [replytoaddress] -codepage [code]
2- using Central Administration:
from System Settings -> E-Mail and Text Messages (SMS) section -> Configure outgoing e-mail settings
in the Mail Settings section, type the SMTP server name, the From address mail,the Reply-to address mail, the appropriate Character set.

you can configure outgoing e-mail for specific web application using the following STSADM command:
stsadm -o email -outsmtpserver [server] -fromaddress [fromaddress] -replytoaddress [replytoaddress] -codepage [code] -url[weburl]

References:
http://technet.microsoft.com/en-us/library/cc263462.aspx#section1
http://technet.microsoft.com/en-us/library/cc772058(WS.10).aspx