Hi Julio, just to confirm, you are composing the replies in Firefox on an AT&T or Yahoo website?

If you are getting this message in a delivery status report, does the message contain any other clues as to what might have gone wrong? For example, is there a problem with the recipient's email address?

If you are getting the message in some other way such as a pop-up alert before the message can be sent, does it provide any other details?

Yes, I confirm. The email address is correct. Message follows: MAILER-DAEMON@yahoo.com <MAILER-DAEMON@yahoo.com> To:blancojr@sbcglobal.net Aug 8 at 10:47 AM Sorry, we were unable to deliver your message to the following address.

<aadamek@santafeopera.org>: 550: Service unavailable

--- Below this line is a copy of the message.

DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sbcglobal.net; s=s2048; t=1565282867; bh=8hG4/+jKQovMhcgtSorQCPRZ+W8jFKnN/4adsFoziQg=; h=Date:From:To:In-Reply-To:References:Subject:From:Subject; b=PtyY0iS1Fx2VBk95HLsspbcg2J3ytfVir0X5POpQ42ObXbEWrkUOXFjWbrJWIpm4pQdGilVu+XLxUTkyxeUKF8XK5vbRjdfnCaWeI1tGOrhf+92H1vhfcJiYzgN/LMJTt+yZyPOYqXYrBk9qkDW9Zv+qk+YqhYqoETu7bm1mFsoRoxuo5CnWYI94CxLZ8tSFSSqQi93qPTFB/W/RXWxiZQ1oybJCR9eUjTT20vXakUh5NqGkw8KFOI44ze32k7ECUoR0MXTLrl3K7h4GUI8URXuy3BahAQMHyMvaQ8pqbexLXJPrvg4328n35yykBfw8eflEnzFRKjqXNsCGgxYLsw== X-YMail-OSG: H22pLwcVM1kQlo_yHJflsqizlDtN9Jbx0fgPu2O6vLlTvZKjixrM07imEP_7Zqv 4O_rY_rVrHHkVO6CvgQrKfPk2gKSa1gm1srcTW8hF9750kwfBXc9lTLYu808QbpUDdgEKyvQezhY iD06HnUCm0yL50ciYRPDpcicOtYpsRE7PPiVJBKIlOV1YI6EFyd.MY6DicahTk.KLToKedMkEcSE tZEtlHdduweiK0L7gm2ajs6S6PPUYPVMnc_KyjYbetldv9CBHa_i_TeGEzrB13cPlhBJRBZ7MUNZ kI4mAlJSW0rFI6xQvRao0ypXQQBqI3e9FNdml8NyABHuu68JoVpp8a3EBZ_VMYrjLBTMTt3dfg2B xFT6UZAHPphZ8dle9Irh1kyDbybC23g42R.wedyX0IdCjyAtilWWzhZPUdZxA9qq_PQw0h_tcg8X 3CMkufAFnpLKNCOHQr7w6vgMXm7vwGxlpduvcy2DeKb5kB9VD2qVaKBa_7HCN5OvgHWL4LVvZ8Yz xbw1KmJH_o1TIDEeRMuRXvMvZoeW8NqpYvO_WPI0oR.tcoT1MBMnRgM96ZwM2C.f25V7oMNQVV8t VJOxxlWlJhx.gFN9jpY.hx4DraPSE9MP29PGfLgg.iRsa5ALQZ93pndkTl0T2Wwim_G4oF73rm4_ 9OYKQq.XhM.wDhhS2TUR8JbeHsKeEXAIIIqfczk3Jx28GqKEEICFsjpYSaLkg72WuWCZaLLqDK2j CRFzK20M3Ni9T9w.ojG.U_aLwwyB0e3doPI5s5nlmPRavs4GN6F5gIf4RScHCCKMH2C427GOqTuO r8XXT.BcRn4qFmN6fuD56AK2yPtupq48iX7yjvwiGeeLEGJhvTLR0zAEkU2zeo0FSCKEd4FxFrm9 0btBPkaBl4MmPJmnN_cVwGP1OWHaGmupRPSUzhBnhpa8KpASq20.9OrBsJq_nSl.3xCQrIyuG8dK pzTT.EMwCVik1xpow17B0jzJ4RGF.FGvdtgq2CK8vbjdqjaD4sZOgjTTxQRPv4aecioa_3AqGrXA R1gBV7qNxlRg2V49TV8.r_OiIfio9U2CSwTBHVTA9wQjFcTsd_FHsKnPBMArmgagOXZi.r1EThwd sL0NO3uupNLOpZrFsFCYHteGcY5EiAdxUGuhuDMvxxv2L4.01g3jW_dHX.jZk.rzH6D91lUj1iIA SGMHpDANnfwIuBrk9ipNT.TkID5ZhfrivBLKzqCn5w.zaggE4VZOyeV6dIdccSvlyG.4jRZ_mxke uFxsCMpQ228tlhM4x3CdY Received: from sonic.gate.mail.ne1.yahoo.com by sonic306.consmr.mail.bf2.yahoo.com with HTTP; Thu, 8 Aug 2019 16:47:47 +0000 Date: Thu, 8 Aug 2019 16:47:44 +0000 (UTC)

Hmm, I can't imagine the recipient's server has blocked all sbcglobal email addresses, or all mail coming through Yahoo.

Does it work in other browsers on your system, such as Microsoft Edge?

Yes. It works in all other browsers I tried. Edge, Google.

I am also told now that some emails made through (but not all) and I still get the error message so I can't be sure if the email made it or not. This is new since Windows 10 updated a couple of days ago.

Since Yahoo mail is a web app, I don't know why it would be affected by a Windows update differently in different browsers.

To see whether an add-on might be involved, could you test in Firefox's Safe Mode? In its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, any userChrome.css/userContent.css files, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.)

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" Help button > Restart with Add-ons Disabled
• (menu bar) Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?