‘gnus-article-address-banner-alist’ is a powerful tool for removing the annoying advertisment banners appended to messages by many (usually free, web-based) mail providers. Because the providers change their banners with some frequency, often to advertise a new product or service, it can be very difficult to privately maintain regular expressions to match the banners.

The aim of this page is to provide a home for a community-maintained value for this variable.

    ; Yahoo - This regular expression should be reasonably stable, and
    ;         reasonably safe.
    ("@yahoo\\.com" . "^__________________+\nDo you Yahoo!\\?\n.*\n.*\n")
    ; Hotmail - Not very much can be matched, so this could be dangerous.
    ;           Should be reasonably stable though.
    ;           The other option is to use a much less stable value, and
    ;           update it frequently.
    ("@hotmail\\.com\\|" . "^_________________________________________________________________\n.*MSN .*\n.*\n")
    ; Netscape - Very unstable value, not much else can be done though.
    ;            Unless a more stable value can be found, it seems the
    ;            best way to maintain this is to OR updated regexps with
    ;            this value.
    ("@netscape\\.net" . "^__________________________________________________________________\n.*Netscape Network.*\n.*\n.*\n\n.*AOL Instant Messenger.*\n.*\n")

You can also use the variable gnus-article-banner-alist or banner in the PostingStyles. – MarkusKnittig