David Writes, "I was informed that (a company's domain) was being blacklisted by spambag.org which from my understanding is a dead listing. We are not able to receive emails from the company, and according to our email provider, 1&1, it is because of this dead blacklist. How can that be and how can it be fixed?"
It's true, Spambag is indeed a long-dead blocking list. I reported on this fact way back in 2007. If it's true that Internet Service Provider 1and1 is using the Spambag list, then that is very unwise of them. Sometimes what happens in these situations is that after a blocking list shuts down, they "list the world" - making it look as though every IP address possible is on their list. This is sometimes done intentionally, to make an ISP notice that all of their mail is bouncing, to force that ISP to stop using their list. This is often done out of frustration, because the bandwidth needs associated with running a list can be very large and overwhelming. After the list is dead and gone, the (ex-)blocking list maintainer wants to rid themselves of that ongoing responsibility.
It's also sometimes done accidentally, for example, if a domain expires. Sometimes domain speculators will immediately purchase a dead blocking list's domain, and these domain speculators often use "wildcard" DNS records that cause that same "list the world" problem.
Here's what I'd recommend doing here.
First, confirm that the mail is really being blocked due to a Spambag listing. Contact the person you're trying to correspond with. Have them send you an example of the bounce message. If it doesn't reference Spambag, then perhaps the issue is not what you think it is.
After you have confirmed that the mail is really being blocked due to a Spambag listing, contact your ISP and tell them that they need to disable this spam filter. It's defunct, and your ISP is probably accidentally blocking lots of legitimate email due to their continued use of this blocklist in their mail server configuration.
And finally, if necessary, set up a Gmail account and encourage your contact to email you there. I prefer Gmail over other webmails, as while they have great spam filtering, I know from my day job that they rarely block legitimate mails. Worst case scenario, you'll have to go look in the spam folder to find an accidentally-filtered message. It's much less likely that the mail didn't go through due to a spam block, compared to some other webmail providers.