What kind of environment are you hosting your server on? I know that Sourceforge at one point enforced a policy where their servers can only send emails to @users.sourceforge.net.

Thank for reply so fast :)

What kind of environment are you hosting your server on?

plateform = Linux
OS = opensuse
Version 10.2

lamp 1.6.3b

Hi thanks you can mark this post as solved cause,
The problem was that my server smtp.myhost.com refused to send email with address different from xxx@myhost.com.
The solution of the problem was simply to add in the config_inc.php file the line

$g_from_email ='dummy@myhost.com';

so that the email sent by mantis had a domain name compatible with that one of my server.

Thanks again for your help.
Best regards