This has been a problem since the beginning of email. It has nothing to do with Thunderbird. You need to be selective where you post your email address and do not give it to just anyone that asks.

Also: Do not post email addresses in public forums. Do not forward emails without removing the header email address first.

If you forward emails be wary that a recipient may not remove your email when they forward it. So always ask them to remove it first. Forwarded email addresses can end up all over the place and you have no control over it. Often they may contain remote content.

Do not allow 'Remote Content' to be automatically allowed in Thunderbird / email clients. Be wary of automatically having 'Display Inline Attachments' enabled. Hover over email links to see real link display in status Bar before clicking on anything.

There are nefarious people out there who will abuse other peoples' email addresses.

Never respond to any of those received emails. If you know the person whose email address has been abused, warn them about the emails you have received. They may need to warn their family and friends not to respond to any they receive.

I would ask your relative to also scan their computer, just in case someone has accessed their computer or used a keylogger program to get information. Once sure computer is clean, I would advise they change their passwords.

thank you for the answer. I wonder why this problem can not be solved, since this a dangerus part of the e-mail. regards from Germany and thanks again for your time Hans J. Ziegler

re : I wonder why this problem can not be solved,

Because some people are not as respectful of other peoples information and there is nothing you can do about what those people choose to do. Eventually, they usually get bored and do it to someone else.

The difficulty is knowing how they got the inoformation in the first place. You can only do your best to keep personal information private.

You would be amazed how many people post email addresses on public forums or forward emails funny emails to friends without removing private data or without considering whether the email contained remote content.

The bottom line is that is nothing to do with Thunderbird. Just do your best to stay safe.

thank you for your information. Best regards. Hans