re :IP xxx.xxx.xxx.xxx is not permitted to send messages.

Found similar issue here: http://forums.xfinity.com/t5/Email-Web-Browsing/421-Error-when-sending-email-IP-address-is-not-permitted-to/td-p/3092924

For some reason comcast is blocking your router IP address. router needs a new IP address. Try using a new IP address. https://superuser.com/questions/1226862/change-public-ip-address https://www.wikihow.com/Acquire-a-New-IP-Address

Here is another similar question with the same error message. https://support.mozilla.org/en-US/questions/1219421

I contacted Comcast again and, after a couple of days, I got a voice message saying they could not find any problem. I tried to send email to the Comcast server and it works. This follows the same pattern of the previous week - I call Comcast and have the problem escalated and I get a call a couple of days later that it has been fixed. It works and then it doesn't. We'll see how long it works this time. It does look like this might be a more widespread problem than the support staff were willing to admit. The problem with aplus server remains the same.

Just tried outgoing mail and it has failed again with the same error with an IP that is different from the previous error. Since 5/17 when I started tracking this, all of the IP addresses in the error message have been different (since I use a VPN, this is not surprising). The problem exists with or without the VPN, however. I'm not sure this supports the "IP blocking theory".

Quote... CSI IP xxx.xxx.xxx.xxx is not permitted to send messages.

How do you figure this is a theory when the server states the above?

As I mentioned, there have been at least 5 different IP servers mentioned in the error messages that I have experienced in the past couple of weeks. The error message says that the IP is not permitted to send messages but I don't know what that means in practical terms. The error message pops up pretty quickly but I don't know where the block would originate. The error message also mentions an invalid greeting. Don't know what that means in practical terms. My ignorance of the details of email processing is frustrating. My use of the word "theory" was meant to be cute and I did not mean to offend. I certainly appreciate any assistance I can get on this. Can you give me more details as to why you think Comcast is blocking these IPs so I can discuss this with them?

I've tried to locate some information: The error message mentions 'CSI' , this stands for 'Cloudmark Sender Intelligence '. Comcast use it to stop spam.

When you get the error message, is there a number at the start of error message which begins with 'BL' or indeed any number ? https://postmaster.comcast.net/smtp-error-codes.php

https://csi.cloudmark.com/en/reset/

Toad-Hall - Thanks for the info on CSI. I can use that in my discussions with Comcast. To your question, the error messages do not include any codes at all. My original post includes an example of the entire error message that I cut and pasted. I hope I don't have to call Comcast every time I want to send email through Thunderbird. I'm starting to suspect the VPN may be an issue since it would seem more likely that spammers might use the same VPN servers and therefore get the IP blocked. Any other suggestions would be welcome.

re :I call Comcast and have the problem escalated and I get a call a couple of days later that it has been fixed. It works and then it doesn't.

This suggests there is nothing wrong with your settings otherwise you would never get through.

Do you have an xfinty account with comcast? Is comcast your Internet Service Provider ? Did comcast provide you with router?

Test: check to see what is your current IP address. Send email and when you get error, does IP address mentioned in error match your IP router address. then recheck your IP address to see if it has changed.

this will tell you if the IP address is your router IP address.

Who provides you with VPN?

I use Xfinity and I use a VPN. I have been keeping track of the IP addresses that show up in the error messages and they are all VPN server addresses. They are differ with each error occurrence. I thought that I was getting the error even when I turned off the VPN but found that I only "disconnected' it. When I "exited" the VPN, the error did not occur. I am now using one computer with the VPN and another computer with the VPN completely uninstalled to see what happens. My working hypothesis is the VPN servers are now being blocked by Comcast (and at least on other email server that I use).

I think you may well be falling foul of an anti virus product that is not up to your tasks, they are often at the heart of intermittent problems. What do you use?

Although not all VPN's products are the same, and not all providers allow you to actually send mail when using a VPN.

Restart Windows 7 in safe mode with networking and see if you still have an issue.,

Xfinity comcast info on VPN. It mentions various points to check. https://www.xfinity.com/support/articles/using-a-vpn-connection

I now believe that this is not a Thunderbird issue.

I contacted my VPN provider, Private Internet Access (PIA), and they said that they are now whitelisting SMTP servers. They want me to send them the IP address of Comcast's SMTP server. Since Comcast probably has more than one server (maybe hundreds), I suggested to them that they contact Comcast and work it out with them. I also pointed out that they could ping smtp.comcast.net to get the IP. I have not heard back.

PIA says that they have allowed outgoing email through Gmail, Yahoo, Outlook, and a couple of others because those service providers are using spam filters to reduce evil-doer activity. I assume that means that Comcast and Aplus are not using these filters.

My current solution is to disconnect the VPN in order to send email. This is not, of course, what I paid for and I will deal with that.