I'd create a new filter for just that one sender, so as to isolate it and get it working without breaking all the good ones. You can add it back into the blacklist when it has been sorted out. Are there any "funny" characters in the address? Accented, or foreign variants of "regular" characters? I'd have a look at the source of one of the offending messages and see if there is anything odd in the email address that might be affecting the filter trying to match it. Then maybe you can identify a non-contentious portion of the email address and use "contains" rather than trying to match the whole address using "is". As an aside, I have a notion that filters work on the address and ignore the display name. Rather than trying to manage a filter, I use an "is in my address book" filter to match spammy addresses. It's quite easy to add new offenders to this address book, and much easier than editing a filter. You may need the Filtaquilla add-on for the "is in my address book" capability. One downside of keeping an address book for unwanted senders is that by default, appearing anywhere in your Address Book validates an address and it will pop up as a candidate addressee. I work round this by using the MoreFunctionsForAddressBook add-on, which allows you to associate selected address books with each account for the purposes of autocompletion of addresses. So you use this to exclude the spammy address book.