Vanadium 50 said:
It might be necessary to remove the right address.
It might be an attempt to verify that "we have a live one".
How can you tell? Usually you can't
If you didn't subscribe to the list, haven't ever dealt with the company and especially if you don't recognise the company name, you get a very strong hint that they are collecting live addresses for future use. Or to sell on as verified to be live emails. Playing around on the internet I once came across someone selling sets of verified live email address - 10,000, 50,000, 250,000 of them at about one cent per 10 in the pack. I've seen a few screenshots in news articles about the dark web showing similar sets of email addresses for sale.
Yes, it might be a legitimate company that shares your details with a sister company and said so when you first subscribed. This usually results in regular emails from a known company and are more likely to honour your unsubscribe. But they usually code your email into the unsubscribe button, and it gets passed to their list as unsubscribe. So asking you to enter the email address is often the sign that it is collecting data.
One thing I also do is view ALL emails with images switched off, to avoid displaying the one pixel square tracking image that is coded to include the email address or activate a cookie. I only open images if I trust the sender or think I need to see what the image is. The tracking image does confirm the email address is live.
Even totally honest newsletters use a tracking image. I used to run a newsletter for a club, and at one committee meeting a committee member said he hadn't recieved an important email that required something to be checked before the meeting. I opened the newsletter admin section, and told him what day and time he opened it, and that he then opened it the following evening twice more to check something. Then he looked very embarassed at his feeble excuse for not doing some important work before the meeting. The one pixel image in the newsletter triggered the "email opened" feedback.
We were not spying on him, I used the tracking to work out who was no longer interested in receiving the weekly newsletter - we had a lot of Uni students in the club, and it helped me remove those who had left the uni, changed their email address (I'd check with the office if they were still a member) or were no longer interested in the club, while many others who had left the club still read the newsletter regularly several years after leaving. Clicking the unsubscribe in our case updated your database entry automatically. You didn't enter the email address.