New limit on email exchanges? (Solved)

... my replies are bounced back stating a fatal error has occurred ...

What is the exact error message (minus any email addresses or other personal information)?

Comcast's sending limits are given in https://www.xfinity.com/support/articles/limitations-on-sending-email.

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Thanks for the quick reply.  I reviewed the email limits you pointed to and I am not coming close to those limits. 

Here is the bounced email message:

On September 18, 2022 11:29:27 PM  [Edited: "Personal Information"] wrote:

This is an automatically generated Delivery Status Notification.     

Delivery to the following recipients failed permanently:

*  [Edited: "Personal Information"]

Reason: Permanent Error

... Here is the bounced email message ...

If you do "View Source" on that bounce message you may find additional information. (Hard to believe the Forum security bot zapped the Comcast "mailer-daemon" address. Not like it's a secret! {Sigh!})

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

The email address it zapped was the person I was sending the email to,not a comcast email.  I change the first part of the address to say "someone" but it got zapped anyway.  I was exchanging email with someone at           sbcglobal.net

I am using a mail program so I don't see a view source but I did view the header, which shows the mail path. I've included the header below with the to and from addresses removed:

Received: from resomta-c1p-022589.sys.comcast.net ([96.102.18.236])
 by resdmta-c1p-023853.sys.comcast.net with ESMTP
 id aA99oTm4yINxMaAHBoD5uq; Mon, 19 Sep 2022 06:29:05 +0000
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=comcast.net;
 s=20190202a; t=1663568945;
 bh=X369cQ9jqUn0S4LasKkDNmd4VXgfT+4CQMINcXClyRg=;
 h=Received:Received:From:To:Date:Message-ID:Subject:MIME-Version:
  Content-Type;
 b=pfsCCqS17nzmcXE5QxDOl1OHHTFvQrKkewFTyPQ4SWvUJi45GER+sCa6ZV1XNk0BR
  D+G8ZDdF6OCwiQm5SG6AUBrQU6cyIANqYD4uUHqcrD689e4FW12xLe4rM8fGPIa7Qm
  6OnUHcYO3cJscW0ryL1IVyDQnGtbPXFFD/2sz6GIv+nFMbZPb/m3cxdZmyXSFSVDsz
  mCE371QKFU9RiW9fNiNoZ0YgfU/iuEFaqMOc8pfKM6CM/5yGOxc+0edi+yR9PaaALM
  oa0RiosH78IEBcxVPFhkg1O6LVHi13y4tHDQUQiWLPA8rIEtED2LSBgrH/UQsZ0pVP
  Lm2om3Ju0zUUw==
Received: from [10.0.0.27] ([73.241.186.232])
 by resomta-c1p-022589.sys.comcast.net with ESMTPSA
 id aAH2oPZZyI0sYaAH3ouWer; Mon, 19 Sep 2022 06:28:58 +0000
X-Xfinity-VAAS: gggruggvucftvghtrhhoucdtuddrgedvfedrfedviedguddtlecutefuodetggdotefrodftvfcurfhrohhfihhlvgemucevohhmtggrshhtqdftvghsihdpqfgfvfdppffquffrtefokffrnecuuegrihhlohhuthemuceftddunecunecujfgurhephffvfffkjghffgfugggtsegrtdigredtredvnecuhfhrohhmpefmvghvihhnucfvuceokhhtrgguugestghomhgtrghsthdrnhgvtheqnecuggftrfgrthhtvghrnhephfeugedvueeuiefhieetffejhffhvefgtedvvdfhuddtleelhffftdeuffevvdehnecukfhppeejfedrvdeguddrudekiedrvdefvdenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhephhgvlhhopegluddtrddtrddtrddvjegnpdhinhgvthepjeefrddvgedurddukeeirddvfedvpdhmrghilhhfrhhomhepkhhtrgguugestghomhgtrghsthdrnhgvthdpnhgspghrtghpthhtohepuddprhgtphhtthhopegtrghrohguihesshgstghglhhosggrlhdrnhgvth
X-Xfinity-VMeta: sc=0.00;st=legit

From: [removed]
To: [removed]
Date: Sun, 18 Sep 2022 23:28:55 -0700
Message-ID: <183546f7858.27fe.9038467d528df7e2bb72b1e711471049@comcast.net>
In-Reply-To: <1UbwbVZp9j.4dsmfICbzo1@desktop-rd4ps1d>
References: <1UbwbUsYRY.1TxDsTGzMfV.ref@desktop-rd4ps1d>
 <1UbwbUsYRY.1TxDsTGzMfV@desktop-rd4ps1d>
 <183543797a8.27fe.9038467d528df7e2bb72b1e711471049@comcast.net>
 <1UbwbV4sDi.2JeoT8vSycr@desktop-rd4ps1d>
 <183544d8108.27fe.9038467d528df7e2bb72b1e711471049@comcast.net>
 <1UbwbVCozX.3MvvFOSylHN@desktop-rd4ps1d>
 <183545bd8e8.27fe.9038467d528df7e2bb72b1e711471049@comcast.net>
 <1UbwbVZp9j.4dsmfICbzo1@desktop-rd4ps1d>
User-Agent: AquaMail/1.38.1 (build: 103801197)
Subject: Re: Rainy day today
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="183546f796f332d27fe21376e1"

Another thing I just noticed when looking into this.  The comcast email account is set up to use pop3, the Yahoo email account, where things work is using imap.   What I don't understand is that the comcast account works fine for the first 4 to 5 email exchanges before it starts bouncing subsequent email replies.

The headers don't help us here as the "reason we rejected your message" information is typically an attachment in the body of the email. Some mail programs/apps call "view source" by other names. For example Thunderbird calls it "Message Source". What program or app are you using?

The final 6 lines in the first post in https://forums.xfinity.com/conversations/email/temporary-failure-mailerdaemoncomcastnet-multiple-emails/602dafcfc5375f08cd181383 is the kind of thing we're looking for.

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

Yes, I just added a post below the header entry. I believe this is what we are looking for:

Final-recipient: rfc822; [nobody At sbcglobal.net]
Diagnostic-Code: smtp; 553 5.3.0 flph837 DNSBL:RBL 521< 96.102.19.45 >_is_blocked.For assistance forward this error to [Edited: "Personal Information"]

Last-attempt-Date: Sun, 18 Sep 2022 01:12:19 +0000

Seems like somebody thinks it's an invalid address after I send a few replies to it.

Thanks Bruce. I'll do that and see what they say.

FYI the IP address in that error message is assigned to a Comcast mail transfer agent (mail server). See https://postmaster.comcast.net/outbound-mail-servers.html. But I still don't know what ATT's beef with it might be.  :-(

I contacted AT&T and they corrected the problem on their end.

Thanks for the support Bruce!