Simply if the email address comes back to you saying undeliverable, then you have either mispelled the email address or it is invalid. I know I have sent alot of emails to friends that I know have valid email addresses and they have never gotten it. It's somewhere out there in email cyberspace I guess. This error message can occur if you're trying to use email addresses without a domain such as
. on a corporate internet. Thunderbird expects the full email address. Try to keep up to date with your contacts so their email address stays current.
