eZ publish allows dashes in the mail address, however it can be that some e-mail gateways does not support it. What if you try to send it using the 'mail' command?
Alright, it might just be the gateway, its not totally impossible.
However, would you please elaborate a little on the part about trying with the mail-command? Do you mean that I should change the SMTP-settings for eZ in some way? Or just to try to send a mail via an ordinary php-page using php:s mail command?