What I am seeing is a use of UTF characters in the mail subjects and senders, so while you read the word as transunion it may be in the text with an umlaut (ä) or other minor addition.

Open the message in source form (ctrl+U) and copy the text from the From: header into your filter and see if that works better.

Remember to Ctrl+C copy and Ctrl+V paste windows shortcuts. They work in almost all editable text boxes even if there is no menu.

Have you tried using their unsubscribe link from their commercial email? While there is a lot of consumer fear about using unsubscribe links and stories about them confirming legitimate email addresses. Almost all of it is old wives tales and urban myths. Just as people think opening spam confirms their address. It does not. Although loading remote images in the mail can and that is why Thunderbird does not load them by default.

This however is a US company so would have to comply with the US legal requirement to offer an unsubscribe option. I assume you made the initial mistake of not deselecting the option "Please send me helpful tips & news about my service, including special offers from TransUnion and trusted partners!" that they auto select on their check your credit score page. Perhaps you might ring their toll free support line and ask them to help you unsubscribe https://membership.tui.transunion.com/tucm/support.page?

Excellent idea about 'hidden' characters. Thanks. Just for the record, I did not have any selections; these jerks were hired by the state of SC to take care of me because the state records were hacked. I have tried for 3 months to unsubscribe; each time I get a solicitation. I am completely ignored. The hope that a US company would comply with legal requirements is about the same hope that robo callers with abide by the no-call list. There phone support essentially does not not answer; I get a series of automated responses about press 1 for this and 2 for that and another layer of automation and then please login.

There emails are "no-reply ..". I sent an email to their socalled Customer Service but got no reply. . I will try to look at the source. I am sure I will get another one.

It is TruIdenity. Caution to anyone reading this

The suggestion to look at the message source was very interesting. Both the From and Reply to had the form <(nonsense)=transunion.com> where the nonsense was a long string starting with ?. I tried using either string in the message filter without success. Then I tried Contains ? but this didn't work either. These jerks are deliberately and maliciously stopping attempts to block their damn spam.

Requests to unsubscribe via internet or phone don't work.

Don't know where to go next.

welcome to the joy of unicode email addresses. unfortunately Thunderbird does not do well filtering those. (the ? is the clue)

I suggest you use another message header to filter on.

Perhaps the message ID contains their domain name, or the received files.

ANything that appears in the header with a name and a colon like Reply-To: can ne used in a filter. you just have to add the item using customize on the bottom of the drop down in the new filter dialog.