Mail Server Configuration

[sarfaraz_ic]

Dear All,

I am having email server hosted on by name mail.xyz.com so my email address looks like sarfaraz@xyz.com. I have a small office with lan and my staff also have the email IDs on same server.

When i send any email to my office staff it goes to Internet server then comes back to my office. So I want to setup small mail server in my office which will synchronize my Internet mail server timely, and it should perform following tasks...

1. If I am in my office and I send mail to any one @xyz.com it should reach the concern mail box rather than going to Internet mail server.

2. Similarly the server should get sync. with Internet mail server so that person on it office can access the mails.

3. If I send any email to any internet address it should directly reach to that internet address, it should not get stucked in my office mail server.

4. All mails on my Internet mail server should get downloaded on my office mail server for all users on specified time and date.

Please help me in setting up the above senario and would like to know which software will server the best. My Internet mail server is based on Linux.

Thanks in Advance
Sarfaraz