You don't say if your email client is Thunderbird mobile or desktop! If you use Thunderbird's desktop client, it features built in spam filtering capability. You can find a [https://support.mozilla.org/en-US/kb/thunderbird-and-junk-spam-messages guide here]. Most email providers also support server side filtering, typically configured on their webmail settings page. You can add a rule to automatically delete or move emails into the spam folder, based on criteria such as keyword or email address. Rules applied server side are reflected on all clients including webmail, desktop and mobile. Thunderbird for Android doesn't provide built-in email filtering, so server side spam rules are better suited when mobile is used.