You could notify your email provider of the issue. This might also be the sender's problem if these error occur when sending to a large list of recipients.

David - thanks for your thoughts, but when I contacted Talktalk, they suggested I contact Thunderbird. The sender was sending only to me.

That is an example of the level of support some email providers give. No email client could ever give that error message. The message is being generated by a TalkTalk server. I did a quick web search on this error message and noticed there are others out there who report to their email provider and are ignored. In this case, Thunderbird isn't even involved. Message goes from the sender's email server to the TalkTalk server which responds back. They are ignoring the problem.

Unless any other suggestions are received, perhaps I need to go back to Talktalk, and hopefully get a different "adviser".

Yes, if there is web access to the message, tell them it's not coming there. Don't even mention Thunderbird.