If it were always the same "someone" then it would be trivially easy to set up a filter to handle those messages. But you would have an unusually inept spammer if that were the case. If they are stupid enough to be actually using the word ''viagra'' in the subject line then it would again be trivially easy to create a filter for that. https://support.mozilla.org/en-US/kb/organize-your-messages-using-filters Whatever you do, I suggest you continue marking any such messages as Junk if Thunderbird is not doing so already.

Thanks a lot. Hope this works.