Have you contacted Mindspring about the fact Google are now refusing their emails because they have failed to correctly configure their mail server in the DNS system?

There is nothing to say the Earthlink web mail actually uses any of the same infrastructure your SMTP server you send via using Thunderbird does. I am see more and more ISP mail where is does not, and the technicians often do not even know the legacy SMTP servers are still used. I think it has something to do with most US based companies hiring Microsoft trained folks and the Microsoft proprietary systems do not use SMTP. So you need to talk to the folk that have not managed their system correctly.

Mindspring (Outlook) email is NOT being refused by Google. As I stated, IF I send an email through Mindspring' webmail page, it goes through.

IF I send the same email to the same address via Thunderbird, it does NOT go through, it gets kicked back with the error message as stated above. Thunderbird IS sending it through Earthlink's perimeters and settings, so it is not going through any other mail server. How is it then that Earthlink, using SMTP still can send my email through, but Thunderbird using the same SMTP, can't?

If Mozilla no longer plans to support Thunderbird, Let me know NOW.

You are misunderstanding Matt's helpful comments. SPF and DKIM problems are with the email provider's server setup. This problem is not being created by Thunderbird and cannot be fixed by Thunderbird. You need to notify Mindspring of the issue. We have seen recently that other email provider's emails are being rejected for the same reason and it appears that Google is hardening down on security.

Tell me them, How is Mindspring going to change settings for Thunderbird to work, IF it already works with their webmail? I will contact them, but what if they simply say "Hey, it works with our webmail!" What exactly do THEY have to change to get Thunderbird to work?

There are several internet sites that explain the techniques for that. It works for their website because they know they own the server. But Google does not own their server and Google looks for ownership information on the server. Try to access the same email account with another email client and you will encounter the same error. It's not Thunderbird.

OK I appreciate hearing that it won't work on other email apps...Saves me the trouble of trying. I'll contact Earthlink and tell them to ficxi it,

Thanks

To begin gmail is increasing its authentication processes for sound logical reason, ie, protecting against scammers pretending to other than who they are. Hence, Verisign explained it me along the lines: any reference to an email address needs a current SPF, DKIM or DMARK record or domain. If it has such it can be verified by google/gmail. Verification requires proof of ownership of the underlying domain, ie, bit to the right of the @. Verifying requires a TXT record, which requires the appropriate DNS for that domain. If you using only an ISP email, then that ISP is responsible for verification, on the other hand if the client owns the domain, it isn't the ISP that is responsible it is the client. Maybe in this example Thunderbird is generating an intermediary into the authentication process prior to the ISP, hence could be leading to the authentication challenge, ie, a mismatch between, say the sending and recieving DNS.

Tell me them, How is Mindspring going to change settings for Thunderbird to work, IF it already works with their webmail? I will contact them, but what if they simply say "Hey, it works with our webmail!" What exactly do THEY have to change to get Thunderbird to work?

They have to fix the DMARC setting in DNS to identify the server as a legitimate sender of mail when Google probes the DMARC doing a reverse DNS to ensure the sender is sending from an authorized server for that domain it is getting back that it is not.

Unfortunately your provider might not actually employ anyone competent enough to fix the issue. They certainly will not be working a support phone if they do. You will nee to get the issue elevated to an actual engineer that knows about DNS and DMARC.

The person who answers the phone is paid to read scripts and get you off the phone in the least time possible. Resolution is not in the financial equation that goes with free support. That is why they go can you send from web mail, then all is good. Because that is what the script says to tell you.

I'm not an Mindspring (or Thunderbird YET have raised another thread about that) client, just getting the same issue with my ISP and gmail. Works fine through their webmail but fails from my email host via ISP to all gmail accounts. In my case it is the host, so I've suggested, no more than that, it might be Thunderbird. My non guro thought is, as mindspring.com is the failure, the bit to the right of the @, it is the owner of the second level domain, ie, mindspring... that is responsible for the verification, and hence all the individuals to the left of the @