mail configuration too tight validating sender e-mail address

this is NOT critical and is only personal preference. I tend to have my firewalls set on something like "router.example.local". However, when I put in the sender e-mail address as "root@router.example.local" it is rejected as an invalid e-mail address.

Maybe this is by designed; some spam filters will reject mail with a From: that uses .local as a TLD. If so, ignore this.