Failure in attempts to send to multiple recipients Eudora 7.x

Post by Loi Ber
There has been an error transferring your mail. I said ... and then the SMTP server (outbound.att.net) said: 554.6.6.0 Error sending message for delivery .
- Cleared all ATT and Yahoo cookies, and jumped through hoops revalidating my login information.

Unlikely to be of any import... Eudora does not use cookies

Post by Loi Ber
- Generated a new ATT security password key and replaced my prior password with it.
- Checked my Tools/Checking Mail and Tools/Sending Mail settings for POP3. All are according to ATT. I also have no bad certificates. I also deleted a few expired certificates.

POP3 is not used for sending. Sending is done using SMTP.

Post by Loi Ber
I spent 50 min. with ATT tech support. He seemed proficient and thorough and found nothing in my profile to explain what is happening. He said the problem must be with Eudora. I am wondering if there is a Eudora.ini setting I need to add?

None that I know of... The error message says the server is rejecting
whatever is being sent.

Post by Loi Ber
Any suggestions for a fix? Many thanks in advance.

Enable full logging (have you installed esoteric plugin?) including ALL
BYTES sent/received. Normally SMTP handshaking should be something like

HELO (or EHLO)
MAILFROM your.address
RCPTTO first.destination
RCPTTO second.destination
RCPTTO ...
RCPTTO last.destination
BODY
contents of message -- including headers!
.

--
Wulfraed Dennis Lee Bieber AF6VN
***@ix.netcom.com http://wlfraed.microdiversity.freeddns.org/

DaveH2

2022-03-30 11:59:47 UTC

The email shows up in the DRAFT folder on the ATT/Yahoo email server with all intended recipients stripped out.
In Eudora 7.1.0.9, in my Outbox folder, the message has the "broken envelope" icon in front of the message.
There has been an error transferring your mail. I said ... and then the SMTP server (outbound.att.net) said: 554.6.6.0 Error sending message for delivery .
Fortunately, I can email a single recipient and am having no issues receiving email.
I had already upgraded the SSL to v1.2 a few years ago and haven't experienced a problem like this since.
SMTP port setting is 465.
POP port setting is 995.
Set "Required, Alternate Port" for both incoming and outgoing mail.
Mail server setting: inbound.att.net
SMTP server setting: outbound.att.net
- Cleared all ATT and Yahoo cookies, and jumped through hoops revalidating my login information.
- Generated a new ATT security password key and replaced my prior password with it.
- Checked my Tools/Checking Mail and Tools/Sending Mail settings for POP3. All are according to ATT. I also have no bad certificates. I also deleted a few expired certificates.
I spent 50 min. with ATT tech support. He seemed proficient and thorough and found nothing in my profile to explain what is happening. He said the problem must be with Eudora. I am wondering if there is a Eudora.ini setting I need to add?
The maximum number of people on my mailing list is 18. Even sending to two recipients is failing now.
Any suggestions for a fix? Many thanks in advance.

Very strange that the messages are ending up in the drafts folder on the server, especially if Eudora is saying that they weren't sent! I suspect that's because the server didn't tell Eudora they had been sent. Are you absolutely sure that the entries listed in the 'To:' field on the message in Eudora are formatted correctly, that is to say with a comma immediately after each one, followed by a space? Eudora will normally tell you if that's wrong, but you never know! Do you queue messages before you send them? If not, try that and see if Eudora then says there's anything wrong.

Dennis Lee Bieber

2022-03-30 15:20:06 UTC

Post by DaveH2
Very strange that the messages are ending up in the drafts folder on the server, especially if Eudora is saying that they weren't sent! I suspect that's because the server didn't tell Eudora they had been sent. Are you absolutely sure that the entries listed in the 'To:' field on the message in Eudora are formatted correctly, that is to say with a comma immediately after each one, followed by a space? Eudora will normally tell you if that's wrong, but you never know! Do you queue messages before you send them? If not, try that and see if Eudora then says there's anything wrong.

I apparently missed that aspect but to me that just adds more
confusion.

An SMTP server doesn't HAVE mailboxes per se ("draft" or otherwise).
SMTPd is solely concerned with receiving messages from clients (or other
SMTPd relays) and forwarding them to the destination (MX) server. The final
SMTP server in a chain drops messages into the email account "inbox" --
which is just a file (MBOX) or directory (MAILDIR) from which email clients
can fetch them (POP3) or directly access (if the client runs on the same
machine as the email account mailbox). {Back in the days of my Amiga, my
first email clients ONLY accessed local mailbox files -- I had to have
scheduled jobs handling "sendmail" (SMTP) duties, and "fetchmail" (POP3).
This was back in the days when one could connect to practically any SMTP
server, and so long as either the MAILFROM or /at least one/ RCPTTO address
was hosted by the server, it would be accepted and relayed.}

IMAP servers OTOH attempt to keep all user mailboxes on the server
side, replicating the contents of any client-side mailboxes. IMAP uses a
different protocol -- replacing both SMTP and POP3.

Eudora does not do IMAP!

I'll reiterate that my recommendation would be to (if needed) install
the esoteric plugin, then set full logging in Eudora. Attempt a send,
shutdown Eudora, and examine the log file for the handshaking being done...

Wed Mar 30 10:58:45 2022
Version 7.1.0.9
LogLevel 44959 (0xAF9F)
Mode 2
MAIN 256: 0.00 Plugin: Checking path
C:\Users\Wulfraed\AppData\Roaming\Qualcomm\Eudora\Plugins.

<SNIP>

17432 8192: 0.02 Msg 7 hash 1988260857 gmt 624428DB flags 0x118C f R K s t
MAIN 16: 2.34 Preparing messages to Send: 1
MAIN 16: 2.34 RSET
MAIN 16: 2.34 MAIL FROM:<***@ix.netcom.com>
MAIN 16: 2.34 RCPT TO:<***@ix.netcom.com>
MAIN 16: 2.34 RCPT TO:<***@earthlink.net>
MAIN 16: 2.34 DATA
MAIN 16: 2.34 Test message
MAIN 16: 2.34 Preparing messages to Send: 0
14788 16: 2.34 Open 51.81.229.172:587
14788 64: 2.35 Rcvd: "220 Welcome to smtp.oxsus-vadesecure.net ESMTP
oxsus2nmtao01p smtp\r\n"
14788 32: 2.35 Sent: "EHLO ElusiveUnicorn.ix.netcom.com\r\n"
14788 64: 2.35 Rcvd: "250-smtp.oxsus-vadesecure.net ESMTP oxsus2nmtao01p
smtp\r\n"
14788 64: 2.35 Rcvd: "250-AUTH LOGIN PLAIN\r\n"
14788 64: 2.35 Rcvd: "250-STARTTLS\r\n"
14788 64: 2.35 Rcvd: "250-8BITMIME\r\n"
14788 64: 2.35 Rcvd: "250-PIPELINING\r\n"
14788 64: 2.35 Rcvd: "250-HELP\r\n"
14788 64: 2.35 Rcvd: "250-CHUNKING\r\n"
14788 64: 2.35 Rcvd: "250-BINARYMIME\r\n"
14788 64: 2.35 Rcvd: "250 SIZE 52428800\r\n"
14788 32: 2.35 Sent: "STARTTLS\r\n"
14788 64: 2.35 Rcvd: "220 Ready to start TLS\r\n"

<SNIP><a whole bunch of hex representation>

<Following is, I think, the translation of the snipped hex stuff>
<This is the SMTP handshake data -- I've obscured where a
password would be send>
<Apparently, after starting TLS, the client has to reintroduce
itself to the server>

14788 32: 2.37 Sent: "EHLO ElusiveUnicorn.ix.netcom.com\r\n"
14788 64: 2.37 Rcvd: "250-hello TLS\r\n"
14788 64: 2.37 Rcvd: "250-AUTH LOGIN PLAIN\r\n"
14788 64: 2.37 Rcvd: "250-XCLIENT ADDR\r\n"
14788 64: 2.37 Rcvd: "250-8BITMIME\r\n"
14788 64: 2.37 Rcvd: "250-PIPELINING\r\n"
14788 64: 2.37 Rcvd: "250-HELP\r\n"
14788 64: 2.37 Rcvd: "250-CHUNKING\r\n"
14788 64: 2.37 Rcvd: "250-BINARYMIME\r\n"
14788 64: 2.37 Rcvd: "250 SIZE 52428800\r\n"
14788 32: 2.37 Sent: "AUTH LOGIN\r\n"
14788 64: 2.37 Rcvd: "334 VXNlcm5hbWU6\r\n"
14788 32: 2.37 Sent: "obscured\r\n"
14788 64: 2.37 Rcvd: "334 UGFzc3dvcmQ6\r\n"
14788 32: 2.37 Sent: "obscured=\r\n"
14788 64: 2.38 Rcvd: "235 Authentication successful\r\n"
14788 32: 2.38 Sent: "RSET\r\n"
14788 64: 2.38 Rcvd: "250 OK\r\n"
14788 32: 2.38 Sent: "MAIL FROM:<***@ix.netcom.com>\r\n"
14788 64: 2.38 Rcvd: "250 OK\r\n"
14788 32: 2.38 Sent: "RCPT TO:<***@ix.netcom.com>\r\n"
14788 64: 2.38 Rcvd: "250 OK\r\n"
14788 32: 2.38 Sent: "RCPT TO:<***@earthlink.net>\r\n"
14788 64: 2.38 Rcvd: "250 OK\r\n"
14788 32: 2.38 Sent: "DATA\r\n"
14788 64: 2.38 Rcvd: "354 Ready\r\n"

<The following is the body of the message -- including headers>
<Note that the TO: header is only used by Eudora to provide the
above RCPT TO data -- spam emailers don't care what the
TO: header contains, they just read a list of email addresses
and send RCPT TO handshakes to the server>

14788 32: 2.38 Sent: "X-Mailer: QUALCOMM Windows Eudora Version
7.1.0.9\r\n"
14788 32: 2.38 Sent: "Date: Wed, 30 Mar 2022 11:01:15 -0400\r\n"
14788 32: 2.38 Sent: "To:
***@ix.netcom.com,***@earthlink.net\r\n"
14788 32: 2.38 Sent: "From: Dennis Lee Bieber
<***@ix.netcom.com>\r\n"
14788 32: 2.38 Sent: "Subject: Test message\r\n"
14788 32: 2.38 Sent: "Mime-Version: 1.0\r\n"
14788 32: 2.38 Sent: "Content-Type: text/plain; charset="us-ascii";
format=flowed\r\n"
14788 32: 2.38 Sent: "\r\n"
14788 32: 2.38 Sent: "\r\n"
14788 32: 2.38 Sent: "Just a test message to examine log file.\r\n"
14788 32: 2.38 Sent: "\r\n"
14788 32: 2.38 Sent: "\r\n"
14788 32: 2.38 Sent: "-- \r\n"
14788 32: 2.38 Sent: "\tWulfraed Dennis Lee Bieber
AF6VN\r\n"
14788 32: 2.38 Sent: " \r\n"
14788 32: 2.38 Sent: "***@ix.netcom.com
http://wlfraed.microdiversity.freeddns.org/\r\n"
14788 32: 2.38 Sent: "\r\n"
14788 32: 2.38 Sent: ".\r\n"
14788 64: 2.38 Rcvd: "250 2.6.0 Message accepted with ID
8ab98b0e-16e130b2a8f2e0e8\r\n"
14788 32: 2.38 Sent: "QUIT\r\n"
14788 64: 2.38 Rcvd: "221 Goodbye\r\n"

That ".\r\n" is how the server is told that the last line of the body
has been sent.

--
Wulfraed Dennis Lee Bieber AF6VN
***@ix.netcom.com http://wlfraed.microdiversity.freeddns.org/

Jim H

2022-03-30 16:31:37 UTC

On Wed, 30 Mar 2022 11:20:06 -0400, in

Post by Dennis Lee Bieber
Eudora does not do IMAP!

The Eudora User Manual doesn't agree with you.

--
Jim H

Piet

2022-03-30 19:13:55 UTC

Post by Dennis Lee Bieber
Eudora does not do IMAP!

The Eudora User Manual doesn't agree with you.

Neither do I. Eudora and IMAP have been happily married
for many, many years.

-p

Dennis Lee Bieber

2022-03-30 20:46:14 UTC

On Wed, 30 Mar 2022 21:13:55 +0200, Piet

Post by Dennis Lee Bieber
Eudora does not do IMAP!

The Eudora User Manual doesn't agree with you.

Neither do I. Eudora and IMAP have been happily married
for many, many years.

Okay, I was focused on the outgoing server, not incoming server,
properties (I've never used an IMAP configuration).

The fact that IMAP is shown only on the incoming server settings still
would have me concerned, and I'd still want to see the actual logging being
done when trying to send a message.

I could visualize the IMAP side trying to synchronize Eudora's OUT
mailbox with an IMAP server "draft" mailbox...

--
Wulfraed Dennis Lee Bieber AF6VN
***@ix.netcom.com http://wlfraed.microdiversity.freeddns.org/

Scratch baker

2022-03-30 21:16:54 UTC

Post by Dennis Lee Bieber
Eudora does not do IMAP!

The Eudora User Manual doesn't agree with you.

Neither do I. Eudora and IMAP have been happily married
for many, many years.
-p

I am not using IMAP, am using POP3. Just had another hour on the phone with ATT who claims my account is totally secure and working fine. They also affirmed that my POP3 settings are correct. I called them after receiving a pointless email saying I should change my password (did that several days ago during troubleshooting) and "remove any type of spam locks". The ATT tech support did not know what that means and said I should ignore it. Still hoping for a solution...

DaveH2

2022-03-30 23:37:33 UTC

Post by Scratch baker

Post by Dennis Lee Bieber
Eudora does not do IMAP!

The Eudora User Manual doesn't agree with you.

Neither do I. Eudora and IMAP have been happily married
for many, many years.
-p

So are you selecting your recipients from your Eudora address book by selecting them all in the list and hitting the 'To:' button?
That should definitely put them in the 'To:' field of the message correctly, with a comma after each one followed by a space.
Please check that this is happening correctly. Try with a dummy message, you don't have to actually send it!

Scratch baker

2022-03-31 03:27:32 UTC

Post by DaveH2

Post by Scratch baker

Post by Dennis Lee Bieber
Eudora does not do IMAP!

The Eudora User Manual doesn't agree with you.

Neither do I. Eudora and IMAP have been happily married
for many, many years.
-p

RESOLUTION! After getting a terrible, inappropriate suggestion from ATT "support" to "to remove any type of spam locks" which I could not decipher, I called ATT Tech Support and that person didn't understand what "to remove any type of spam locks" meant either. Then I backed up, deleted, and reinstalled Eudora. Still had the problem. I googled "cannot send bcc email on att.net" and got this hit at the top of the list https://support.mozilla.org/en-US/questions/1372359. It was not just me!

As of March 24, 2022, PROBLEM IS: Yahoo will not allow sending of BCC unless there is also a valid To: address. So I sent my email TO myself and BCC'd my list and it sent. I now have created an alias which I already filtered to spam, so I won't be receiving my own messages on the server, but will be able to BCC others to avoid spammers. I also sent email to ATT about not informing anyone, including their own tech support, of the poorly thought out change.

DaveH2

2022-03-31 12:28:29 UTC

RESOLUTION! After getting a terrible, inappropriate suggestion from ATT "support" to "to remove any type of spam locks" which I could not decipher, I called ATT Tech Support and that person didn't understand what "to remove any type of spam locks" meant either. Then I backed up, deleted, and reinstalled Eudora. Still had the problem. I googled "cannot send bcc email on att.net" and got this hit at the top of the list https://support.mozilla.org/en-US/questions/1372359. It was not just me!
As of March 24, 2022, PROBLEM IS: Yahoo will not allow sending of BCC unless there is also a valid To: address. So I sent my email TO myself and BCC'd my list and it sent. I now have created an alias which I already filtered to spam, so I won't be receiving my own messages on the server, but will be able to BCC others to avoid spammers. I also sent email to ATT about not informing anyone, including their own tech support, of the poorly thought out change.

Well that's news to me as well, it's good to know as my main e-mail account is also Yahoo-based!
I don't BCC people, so I would probably never run into the problem, but it would have really puzzled me too if I had done.
Really glad that you found the cause, and the fact that this restriction was applied and their technical support people were not told about it is really bad!
Cheers, Dave.

Scratch baker

2022-03-30 17:49:28 UTC

Post by DaveH2

I have different books in my Address book and am Bcc'ing the same group of people I frequently contact. I also rewrote one message and only used some of the addresses and the Send still failed. I have about 8 messages that failed, all with the same result (in Drafts folder on server with all recipients missing). I may try a complete reinstall of Eudora if no one comes up with any other suggestions. BTW, I discovered that some old Eudora support pages can be searched on www.archive.org but I still didn't find anything new to try. I had not had this problem earlier in the day. I also shut down my laptop every night, so a reboot hasn't helped either. I also deleted and rebuilt those Address books. Did not help.

Dennis Lee Bieber

2022-03-30 20:57:12 UTC

On Wed, 30 Mar 2022 10:49:28 -0700 (PDT), Scratch baker
<***@gmail.com> declaimed the following:

<SIGH> Apparently another user of Google Groups -- which over the years
has decided that X-NoArchive means "SHOW TO NOBODY AT ANYTIME", rather than
"EXPIRE after a few days"... I'll have to remember to turn it back on in a
few days.

Post by Scratch baker
I have different books in my Address book and am Bcc'ing the same group of people I frequently contact. I also

By definition BCC: headers are REMOVED from the body of outbound
messages AFTER the addresses are extracted and used in the SMTP handshake.
Do you have anything in the TO: field, or are you only providing BCC?

Please set up FULL logging in Eudora and examine the results of sending
a message. The error message you report is coming from the server, it
should not be anything in Eudora itself. Full logging should show WHEN the
error is being reported.

I'm going to repeat content from a previous message -- which Google
Groups deleted instantly... (comp.mail.eudora... is NOT a Google message
group -- it is a USENET newsgroup being mirrored by Google).

I'll reiterate that my recommendation would be to (if needed) install
the esoteric plugin, then set full logging in Eudora. Attempt a send,
shutdown Eudora, and examine the log file for the handshaking being done...

Wed Mar 30 10:58:45 2022
Version 7.1.0.9
LogLevel 44959 (0xAF9F)
Mode 2
MAIN 256: 0.00 Plugin: Checking path
C:\Users\Wulfraed\AppData\Roaming\Qualcomm\Eudora\Plugins.

<SNIP>

17432 8192: 0.02 Msg 7 hash 1988260857 gmt 624428DB flags 0x118C f R K s t
MAIN 16: 2.34 Preparing messages to Send: 1
MAIN 16: 2.34 RSET
MAIN 16: 2.34 MAIL FROM:<***@ix.netcom.com>
MAIN 16: 2.34 RCPT TO:<***@ix.netcom.com>
MAIN 16: 2.34 RCPT TO:<***@earthlink.net>
MAIN 16: 2.34 DATA
MAIN 16: 2.34 Test message
MAIN 16: 2.34 Preparing messages to Send: 0
14788 16: 2.34 Open 51.81.229.172:587
14788 64: 2.35 Rcvd: "220 Welcome to smtp.oxsus-vadesecure.net ESMTP
oxsus2nmtao01p smtp\r\n"
14788 32: 2.35 Sent: "EHLO ElusiveUnicorn.ix.netcom.com\r\n"
14788 64: 2.35 Rcvd: "250-smtp.oxsus-vadesecure.net ESMTP oxsus2nmtao01p
smtp\r\n"
14788 64: 2.35 Rcvd: "250-AUTH LOGIN PLAIN\r\n"
14788 64: 2.35 Rcvd: "250-STARTTLS\r\n"
14788 64: 2.35 Rcvd: "250-8BITMIME\r\n"
14788 64: 2.35 Rcvd: "250-PIPELINING\r\n"
14788 64: 2.35 Rcvd: "250-HELP\r\n"
14788 64: 2.35 Rcvd: "250-CHUNKING\r\n"
14788 64: 2.35 Rcvd: "250-BINARYMIME\r\n"
14788 64: 2.35 Rcvd: "250 SIZE 52428800\r\n"
14788 32: 2.35 Sent: "STARTTLS\r\n"
14788 64: 2.35 Rcvd: "220 Ready to start TLS\r\n"

<SNIP><a whole bunch of hex representation>

<Following is, I think, the translation of the snipped hex stuff>
<This is the SMTP handshake data -- I've obscured where a
password would be send>
<Apparently, after starting TLS, the client has to reintroduce
itself to the server>

14788 32: 2.37 Sent: "EHLO ElusiveUnicorn.ix.netcom.com\r\n"
14788 64: 2.37 Rcvd: "250-hello TLS\r\n"
14788 64: 2.37 Rcvd: "250-AUTH LOGIN PLAIN\r\n"
14788 64: 2.37 Rcvd: "250-XCLIENT ADDR\r\n"
14788 64: 2.37 Rcvd: "250-8BITMIME\r\n"
14788 64: 2.37 Rcvd: "250-PIPELINING\r\n"
14788 64: 2.37 Rcvd: "250-HELP\r\n"
14788 64: 2.37 Rcvd: "250-CHUNKING\r\n"
14788 64: 2.37 Rcvd: "250-BINARYMIME\r\n"
14788 64: 2.37 Rcvd: "250 SIZE 52428800\r\n"
14788 32: 2.37 Sent: "AUTH LOGIN\r\n"
14788 64: 2.37 Rcvd: "334 VXNlcm5hbWU6\r\n"
14788 32: 2.37 Sent: "obscured\r\n"
14788 64: 2.37 Rcvd: "334 UGFzc3dvcmQ6\r\n"
14788 32: 2.37 Sent: "obscured=\r\n"
14788 64: 2.38 Rcvd: "235 Authentication successful\r\n"
14788 32: 2.38 Sent: "RSET\r\n"
14788 64: 2.38 Rcvd: "250 OK\r\n"
14788 32: 2.38 Sent: "MAIL FROM:<***@ix.netcom.com>\r\n"
14788 64: 2.38 Rcvd: "250 OK\r\n"
14788 32: 2.38 Sent: "RCPT TO:<***@ix.netcom.com>\r\n"
14788 64: 2.38 Rcvd: "250 OK\r\n"
14788 32: 2.38 Sent: "RCPT TO:<***@earthlink.net>\r\n"
14788 64: 2.38 Rcvd: "250 OK\r\n"
14788 32: 2.38 Sent: "DATA\r\n"
14788 64: 2.38 Rcvd: "354 Ready\r\n"

<The following is the body of the message -- including headers>
<Note that the TO: header is only used by Eudora to provide the
above RCPT TO data -- spam emailers don't care what the
TO: header contains, they just read a list of email addresses
and send RCPT TO handshakes to the server>

14788 32: 2.38 Sent: "X-Mailer: QUALCOMM Windows Eudora Version
7.1.0.9\r\n"
14788 32: 2.38 Sent: "Date: Wed, 30 Mar 2022 11:01:15 -0400\r\n"
14788 32: 2.38 Sent: "To:
***@ix.netcom.com,***@earthlink.net\r\n"
14788 32: 2.38 Sent: "From: Dennis Lee Bieber
<***@ix.netcom.com>\r\n"
14788 32: 2.38 Sent: "Subject: Test message\r\n"
14788 32: 2.38 Sent: "Mime-Version: 1.0\r\n"
14788 32: 2.38 Sent: "Content-Type: text/plain; charset="us-ascii";
format=flowed\r\n"
14788 32: 2.38 Sent: "\r\n"
14788 32: 2.38 Sent: "\r\n"
14788 32: 2.38 Sent: "Just a test message to examine log file.\r\n"
14788 32: 2.38 Sent: "\r\n"
14788 32: 2.38 Sent: "\r\n"
14788 32: 2.38 Sent: "-- \r\n"
14788 32: 2.38 Sent: "\tWulfraed Dennis Lee Bieber
AF6VN\r\n"
14788 32: 2.38 Sent: " \r\n"
14788 32: 2.38 Sent: "***@ix.netcom.com
http://wlfraed.microdiversity.freeddns.org/\r\n"
14788 32: 2.38 Sent: "\r\n"
14788 32: 2.38 Sent: ".\r\n"
14788 64: 2.38 Rcvd: "250 2.6.0 Message accepted with ID
8ab98b0e-16e130b2a8f2e0e8\r\n"
14788 32: 2.38 Sent: "QUIT\r\n"
14788 64: 2.38 Rcvd: "221 Goodbye\r\n"

That ".\r\n" is how the server is told that the last line of the body
has been sent.

--
Wulfraed Dennis Lee Bieber AF6VN
***@ix.netcom.com http://wlfraed.microdiversity.freeddns.org/

Piet

2022-03-31 09:50:08 UTC

Post by Dennis Lee Bieber

Post by Scratch baker
I have different books in my Address book and am Bcc'ing the same group of
people I frequently contact. I also

By definition BCC: headers are REMOVED from the body of outbound
messages AFTER the addresses are extracted and used in the SMTP handshake.

No. Header and body are separate parts of any e-mail message. And unless
explicitly copied into a body before sending, NO header line will ever
be in the body of a message.
Furthermore, the body of a message is entirely the "property" of the one
sending the message, and NO system between the sender and recipient, nor
the recipients mailbox holding system, should ever make changes to the
body of a message. Which is exactly what Micro$soft hasn't understood.

But since OP talks about "the same group of people", I wonder how many
people that group encompasses. It wouldn't be the first time that a
mail hoster suddenly and drastically reduces the max number of recipients,
and going over that limit can lead to exactly the smtp errormessage this
thread is about.

Also note that addresses are also removed from the To: header line when
the group or named list syntax is used (label:addr1,addr2,...;), which
is a polite alternative for Bcc. It doesn't work though with M$ mailers,
because M$ still lives in the past.

Last but not least: Bcc and group addresses are removed from the header,
but they DO show up in smtp session debugging output, so it wouldn't be
a great idea to post them here, at least not without obfuscating them.

-p

Dennis Lee Bieber

2022-03-31 14:25:38 UTC