Your network contains an SMTP server named server1.contoso.com that runs Windows Server 2008 R2.
You run telnet.exe server1.contoso.com 25 and successfully connect to Server1.
You restart Server1.
You run telnet.exe server1.contoso.com 25 again and fail to connect to Server1.

You need to ensure that you can connect to the SMTP service on Server1.

What should you modify first?

A.
the access control settings of the SMTP Virtual Server

B.
the properties of the Simple Mail Transfer Protocol (SMTP) service

C.
the security settings of the SMTP Virtual Server

D.
Windows Firewall on Server1

Explanation:
Default SMTP service is installed with Manual startup type. Try setting the service to Automatic.