Could you possibly share a sanitized screenshot or header of the emails that fail so we can better troubleshoot where the failure is actually happening?

Info on how to do so here

Problem persists. The first recipient in the list of the group mailing doesn't arrive. I've sent you what you requested. Here's another:

Message will be retried for 0 more day(s)

Technical details of temporary failure: The recipient server did not accept our requests to connect. Learn more at https://support.google.com/mail/answer/7720 [gmail.co 2607:f8b0:4003:c07::13: socket error] [gmail.co 173.194.67.17: socket error] [gmail.co 173.194.67.18: socket error] [gmail.co 173.194.67.19: socket error] [gmail.co 173.194.67.83: socket error]

DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;

       d=gmail.com; s=20120113;
       h=subject:from:message-id:date:user-agent:mime-version:to;
       bh=P0Y3VGn4H6owlp1glVs4vI5qermua7GGWXejOCDnNqA=;
       b=JHy+qobUlbFcIdRSntnYi4kZcqDgC0IxsraXK6slHSLxQxxzKXUHf0BcBaCdxfp5e6
        a/cxcCwPvg+7CCEd3gR4K7DO/FSnipYLWDHoo8SlyLGySn5HhyNx+VFGDRB3vOZ4VzQD
        YqihIhAA1QcHDgrC29JhKlfaA5uiL5naHAdteiWUE6T/9/z6ijqTVDEwYYF/DqNikYbl
        KAgH4P8T1OlMUO/0wrqx4mRb06Gbxmfb0DNc6XVxP4i5/2FGxG2aWcmFnarS+tOKAIDJ
        YQOhnoUySyUcwRRqNseLcqHka9DFI3ZBWgpVA+yeW55vBJmnkU8ultID2Au1U1G/51Kf
        HdxA==

X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;

       d=1e100.net; s=20130820;
       h=x-gm-message-state:subject:from:message-id:date:user-agent
        :mime-version:to;
       bh=P0Y3VGn4H6owlp1glVs4vI5qermua7GGWXejOCDnNqA=;
       b=ZjjIwh4f4LW8iH9eu+YHkFInYphlAbAdAdri6CHcTn1Vs0+JnbxkGpiAGn4ri8Ga1M
        sqaXewiUqq29skWTOdRguhorRT7pfQzRY4UosH1u8zDWgggUyYCw6iSb93RMpp39WiGz
        +pe9PPJSKgjg0CQ4wNsY9rt8IgOm66ja9eShDgCOa40A0pf2oyGhGYpdPnCmiQI/37OT
        Clu6MrjMp6Z2q9atCC83NOP7MI60mPst1hJn/d+dObJvmRm8ym36uzM/eHIY21khp7qD
        gHo5r4H+hSqmBwYGnSB5/m7XDz0crTyoEhXGP8klccyIQlV1LwBNjcA6Ys7sBZw1It7C
        ALgg==

X-Gm-Message-State: AEkoouu31vz/6s465L2LdA6ItdyeqeCl2P8bBuAgQlMoUDwsLepIsapIRGgp3tzeIM8QCw== X-Received: by 10.157.48.16 with SMTP id d16mr29058789otc.63.1469028552901;

       Wed, 20 Jul 2016 08:29:12 -0700 (PDT)

Return-Path: <msalkin@gmail.com> Received: from ?IPv6:2602:301:771c:ff80:30c7:36bb:768a:70a3? ([2602:301:771c:ff80:30c7:36bb:768a:70a3])

       by smtp.gmail.com with ESMTPSA id r62sm1188705oia.25.2016.07.20.08.29.04
       (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
       Wed, 20 Jul 2016 08:29:11 -0700 (PDT)

Subject: Emailing: Girl Talk1.MP3 From: Michael Salkin <msalkin@gmail.com> Message-ID: <dc4b8de5-39d3-b655-b516-e7b2af107c98@gmail.com> Date: Wed, 20 Jul 2016 08:29:03 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101

Thunderbird/45.2.0

MIME-Version: 1.0 To: undisclosed-recipients: ; Content-Type: multipart/mixed;

boundary="------------C335694A7759BC86BC9F7EA7"

All of these IP addresses below belong to Google. [gmail.co 2607:f8b0:4003:c07::13: socket error] [gmail.co 173.194.67.17: socket error] [gmail.co 173.194.67.18: socket error] [gmail.co 173.194.67.19: socket error] [gmail.co 173.194.67.83: socket error]

So I suggest you ask then what the problem is.

I use google's servers for my Thunderbird client but the first address in my group mailing list is not necessarily a gmail address and if I send to those recipients when not in the group mailing the message is delivered. Please let me know if you still believe that this is a google not Thunderbird issue.

Yes I think it is a google issue. It might be triggered by Thunderbird, but only Google could determine what is the cause of the issue. But it is most certainly a Google issue.

When you "send" Thunderbird gives the mail to the mail server and if it receives no error messages about the structure or content of the mail from the mail server it takes down that sending dialog. At that point Thunderbird thinks it has "done it's job" and it has. It has passed the mail to the next link in the delivery chain. Just as once upon a time you wrote an address on an envelope, placed a stamp on it and dropped it into a letter box..

What you are getting is an email from Google telling you they were unable to deliver the mail because of a socket error internal to their network. It is the equivalent of the postal service telling you they could not deliver the mail because their pickup truck had lost the key to the post box you used. (not that they ever did that sort of thing)

The first address is an IPV6 address the following are four IPV4 addresses. As a guess I would say Google have not completely ironed out the bugs in their IPV6 stack so they are experiencing TCP/IP socket errors when translating their IPV6 addresses to IPV4 for transmission.

I have seen a similar issue some 12 or 18 months ago where a US ISP made their west coast infrastructure IPV6 to dip their tow in the IPV6 world and things broke down in talking to their east coast servers using IPV4.

As an experiment, you could try adding the list of recipients to the BCC field in Thunderbird instead of the list name and see if they suffer the same issue.

To add the emails instead of the list name. Click the first in the list Hold shift Click the last in the list. Select the add to BCC button at the bottom

Thank you for your thorough response. My group mailing is always sent as BCC. For privacy sake, I can't alter that. I'll see what google has to say.

A am asking you to change how you add to BCC, not change anything else.

Currently I assume all you see when you compose the mail is the list name in the BCC.

My way you will see however many recipients there are in individual BCC entries. IT only affect how many BCC lines you see and what they show.

I'll give it a try. Done. I'll see if any bounce back and let you know.

Update: Adding the BCC individually instead of by group name sent the initial name normally. I'll let google know what's happening. Other than their forums do you know the best manner in which to contact them?

I must admit I have never done well in their forums or anywhere else. Google is like a black hole to me. everything goes in and nothing comes back out.

I understand!