Below, and attached, is the error that is displayed each time an email is sent from thunderbird on a single PC only that is on a network. The error is for a malformed email that has a "." after the .com Send Message Error ! Sending of the message failed. An error occurred while sending mail. The mail server responded: <removed@removed.com.>: domain missing or malformed sender already given. Please verify that your email address is correct in your account settings and try again. Resolutions attempted: -The malformed email has been removed from the local address book and the error persists -Thunderbird updated to latest version Any advice or solutions is appreciated. Thanks!