We talk about three rather different but not unrelated conjectures here:

(1) Artin $L$-functions are automorphic $L$-functions;

(2) automorphic $L$-functions belong to the Selberg class;

(3) the Selberg class consists of automorphic $L$-functions.

The three families of $L$-functions occurring here are defined very differently. Artin $L$-functions are defined in terms of Galois representations, automorphic $L$-functions are defined in terms of automorphic representations, while the Selberg class is defined via natural axioms of an analytic nature. Conjectures (1) and (2) are instances of the Langlands conjectures, while (3) strengthens the idea that sufficiently nice analytic properties of a Dirichlet series are always "caused by" an automorphic form (or automorphic representation) behind the Dirichlet series.

what is exactly the difference between the Selberg class and the set of Artin L-functions?
I am using Google Apps for Domains to handle my personal email. I have the following filter configured:

Matches: to:(username@example.com)
Do this: Skip Inbox, Mark as read, Delete it


Here is the exported filter XML:

&lt;entry&gt;
    &lt;category term='filter'&gt;&lt;/category&gt;
    &lt;title&gt;Mail Filter&lt;/title&gt;
    &lt;id&gt;tag:mail.google.com,2008:filter:1348992826412&lt;/id&gt;
    &lt;updated&gt;2012-09-30T08:16:38Z&lt;/updated&gt;
    &lt;content&gt;&lt;/content&gt;
    &lt;apps:property name='to' value='username@example.com'/&gt;
    &lt;apps:property name='shouldMarkAsRead' value='true'/&gt;
    &lt;apps:property name='shouldArchive' value='true'/&gt;
    &lt;apps:property name='shouldTrash' value='true'/&gt;
&lt;/entry&gt;


Despite this rule, mail to the username@example.com address is not being matched by the filter. Here is one example headers of a mail that was not caught by the filter:

Delivered-To: username@example.com
Received: by 10.49.35.178 with SMTP id i18csp10155qej;
        Sun, 30 Sep 2012 02:09:09 -0700 (PDT)
Received: by 10.68.225.68 with SMTP id ri4mr32446176pbc.115.1348996149371;
        Sun, 30 Sep 2012 02:09:09 -0700 (PDT)
Return-Path: &lt;b730@mail.tbb.com.tw&gt;
Received: from mail.tbb.com.tw ([210.202.75.124])
        by mx.google.com with SMTP id c5si10659paz.41.2012.09.30.02.09.07;
        Sun, 30 Sep 2012 02:09:08 -0700 (PDT)
Received-SPF: neutral (google.com: 210.202.75.124 is neither permitted nor denied by best guess record for domain of b730@mail.tbb.com.tw) client-ip=210.202.75.124;
Authentication-Results: mx.google.com; spf=neutral (google.com: 210.202.75.124 is neither permitted nor denied by best guess record for domain of b730@mail.tbb.com.tw) smtp.mail=b730@mail.tbb.com.tw
Received: By OpenMail Mailer;Sun, 30 Sep 2012 16:05:41 +0800 (CST)
From: "Loan Financial Private Company" &lt;b730@mail.tbb.com.tw&gt;
Reply-To: micheajoh@w.cn
Subject: Loan Financial Private Company
Message-ID: &lt;1348992338.5369.b730@mail.tbb.com.tw&gt;
Date: Sun, 30 Sep 2012 16:05:41 +0800 (CST)
MIME-Version: 1.0
Return-Path: b730@mail.tbb.com.tw
Content-Type: text/plain; charset=big5
Content-Transfer-Encoding: quoted-printable


Note that I have tens of other similar filters that do properly match mail per address. It is only this one address / filter combination that is failing to match mail.

To proactively address the obvious red herrings and ensure that the discussion remains focused: I am aware of the dangers of posting a live email address publicly. I am aware of Gmail's excellent spam filters. I am aware of the arguments against catch-all email addresses.
