I'm puzzled that Comcast would use a block list against one of its subscribers. If that's what is happening.

Can you rule out the possibility that malware is running on your computer or within your network or through your wireless router that is spewing junk mail and keeping your IP on the block list?

Do NOT have a wireless router. ALL my computers show clean systems. No virus or malware that I know of. Have been having problems with my friends and businesses not getting my emails for a long time. As mentioned above I've been dealing with it by having those people add me to their white lists or address book. In SOME cases that now no longer works. Example .. a friend who has his ISP (cox) can NOT stop my emails from being blocked and he has to use some strange other way to get my emails or something and is frankly tired of the bother. I also have some business accounts and doctors who aren't getting my emails. Seems that the ones that have become a bigger problem lately are those who use Cox.

Now I also having trouble with web sites. Sometimes I have to access some important web sites I use often (like banks or credit cards etc.) using a VPN application to high my IP address. In some cases it is the ONLY way I can pay a bill. And of course using a VPN account has it's own problems. I believe this whole problem can be fixed if comcast would change the personal IP address they assigned me (a few years ago). But after almost two years of my spending HUNDREDS of hours with them after months of waiting the IP is still the same. I've contacted the FTC complained to my congressman and well nothing works. NOW over the last few days I suddenly started having this NEW problem where "thunderbird" has begun to refuse to accept incoming email from some accounts. See the attached screen cap. Changing my ISP is not an option. The actual internet, TV and other service is OUTSTANDING. I like it. And anything even close to it is NOT available where I am. I just a continual and now growing problem which is all about the comcast IP. Please ..I've tried rebooting, changing, modems, and router and even pulling the ower off them for 3 or 4 days. The IP same old blacklisted IP comes back. I've also got rid of several other email applications .. Presently using Thunderbird for the last several months. I'm lost ...

The "Alert from account" message is coming from your mail server at Comcast. It looks like a similar notification to needing an app password for 2FA or hitting a quota. I don't know whether there is a bypass for it in Thunderbird or whether Comcast is now limiting you to webmail. Other forum volunteers may know more.

Do NOT have a wireless router.

As of about 5 years ago I thought all their routers provided wi-fi access to any other Comcast subscriber within range of its wireless signal. But perhaps that doesn't apply to your equipment.

I do not have and have never had anything other than a comcast TV DVR. I have all my own equipment .. Modem, router and home theater PC with TV recording tuners and viewing. My equipment has all been registered and approved by Comcast and all works perfectly. About 2 years ago we started having email blocking problems being reported by my contacts. and it has grown over the last year to become now a serious problem and because of the comcast IP address problem I am starting to have many more new issues. I DON'T do porn EVER, don't visit bad web sites, and use Extensive anti-malware measures as well as practicing safe browsing etc.

FWIW .. I'm not new to the internet. My first computer was a KIT built SWTP computer in the late 60s long before there were PCs ... RAM was measured in K, and storage was a reel to reel tape recorder.

I would have thought things might have gotten better since then .. <grin>

Things have not gotten better in the last 20 years. ISP's actually have become immeasurably less completely and an ongoing process of having everything done externally with the lowest quote means nothing actually works like it should.

To borrow an old quote "American component, Russian component. All made in Hong Kong" The countries have changed around. But the source of electronic bits is all on a budget.

Now unfortunately you are going to have to communicate with the "support" and comcast. Not a pleasant thing as they fail to comprehend that email is more that their web mail offering. My guess is they are saying mail from "domestic" IP addresses is to be blocked because it is spam. All good, except they are blocking their bona fide customers from using the mail server they are paying to use.