This is a note from the guy that wrote the support article on blocking a sender more than a decade ago telling folk how to do it with a filter. https://support.mozilla.org/en-US/kb/blocking-sender

Please post your ideas and feedback in the ideas and feedback forum. It is linked from the Thunderbird help menu as it this one. Blocking a sender may be important to you. I can't really think of anything worse in business that a one click block to creditors sending accounts.

Thanks for this. I have seen that aption. However it is much better to have option to block unwanter sender rather rediecting messages to spam or other folders and get them accumulated in email forders. Other email clients provide this option. I ask Thunderbird team to kindly get this in thunderbird. Thanks

Email Clients are just programs running on your computer and they cannot block emails from arriving on the server. Thunderbird as any other email client can only download whatever is on server. POP accounts only get access to server 'Inbox' to download whatever is in server 'Inbox' and put it in pop account 'Inbox'. So anything the server puts in server 'Spam' folder will never get downloaded to a Pop account. IMAP accounts can subscribe to see server folders and as they synchronise with server folders, the imap folders will display whatever is on server and that includes the Spam folder.

Thunderbird can filter unwanted mail and do whatever you tell it to do eg: put in Spam or directly into the Trash/Deleted folder.

Thunderbird has no control over the server. The server accepts any email sent to you because that is it's purpose. However, you may be able to logon to your webmail account and set up to block a sender.

I have done this in my Gmail webmail account, but even the server will put all blocked senders into the server Spam folder.

There are some programs that can act like a 'middle-man'. There are people who use such programs to act like a filter between server and your email client - aka Thunderbird. As an example: https://mailwasher.net/ I'm not able to advocate the 'Mailwasher' program as I do use it.