You will need to give more information to resolve a problem like that. What operating system, what web server (Windows/IIS, Windows/Apache, Linux/Apache etc etc). What email software, what firewall, any other programs generating email via web apps etc etc.
config.php details might come in useful
I am probably no help at all in solving your problem, but more details might help others.
Installing and upgrading help
Moodle Installation On INTRANET
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