Those sound to me like spam, at least most of them. They are not legitimate. Although there is no way to completely avoid them, Thunderbird has two things that can help mitigate them: - Adaptive Junk Mail Controls. This is what's called a Bayesian filter that learns to recognize spam. You have to train it by marking bad messages as Spam and good messages ad non-Spam. It's not 100% accurate, and it take some training time before it's at its most effective, but it's very helpful. The feature can be enabled for each account at <Account Settings | Junk Settings | Enable adaptive junk mail controls for this account>. - Message Filters. If your unwanted messages can be easily recognized by key words in the Subject, From, To, Body or other criteria, you can create a Filter to automatically move them to the Spam (or other) folder, delete them, or other actions . Here's an article about them: https://support.mozilla.org/en-US/kb/organize-your-messages-using-filters One thing you should never do is respond to such spam messages. That will only tell them that yours is a valid email address, which they will then sell to other spammers to use. Similarly, you should turn off Thunderbird's option to 'Allow remote content in messages'. If this is enabled, the spammer will know you opened their spam and therefore that they reached a valid, sellable address. That setting is found in <Settings | Privacy & Security | Mail Content>.