Resisting spam despite filtering tool

I frequently use the filter tool to transfer undesirable e-mails to the spam box, and it works perfectly well.
Except for one, which resists since months: regrdtfhbftrg.
Does anyone know how to send it automatically to the spam dust bin?

If its from a specific email address, have you tried the option either via the toolbar or right click “Move to folder and Blacklist email address” ?

If you have, then suggest to try setting up a filter like that in your online mailbox server end.