Correction needed? Code is 6.6.0, not 6.6.o. I have the same problem.

This has started happening AGAIN, as of 17th Sept 2019. Last time an update fixed the isseu, but todays update did not. C'mon TBird - sort it out eh!!!

Today it's back a little different: All outgoing emails to groups the same. An error occurred while sending mail. The mail server responded: 554 6.6.0 Error sending message for delivery. donjdool@yahoo.com

This only seems to be happened with Yahoo, but they deny it's anything to do with them. They blame TBird.

Yes the problem is yahoo. You are sending mail without anyone in the To:. YAhoo have made a unilateral decision that that is bad and reject mail that is exclusively send to BCC addresses.

Thanks Matt, ever since Yahoo sold to ?, they have done a number of things STUPID. Think about sending all the negative comments like mine to the President/CEO& all the Yahoo board members.

Hi Don, I've recently had the 'added' 554 to my error report, but still without ANY help from Mozilla whatsoever. It's disgusting that Mozilla is completely unwilling to help, or get involved with this. This same thing happened earlier this year, around March, and was fixed with a TBird update, but this time, nothing!! Mozilla - you should be ashamed. I'm currently looking for another email client. Several people I know use Incredimail, with great success, and are very happy with it. Up yours TBird/Mozilla, stick it where the Sun don't shine!

Amazingly, I had this email from Mozilla 'support' this morning:-

"We just wanted to let you know that luntronjim has found a solution to a Firefox question that you're following.

The question: '"An error occurred while sending mail. The mail server responded: 6.6.0 Error sending message for delivery.. Please check the message and try again."' was marked as solved by its asker, Arvidd.

Did this answer also help you? Did you find another post more helpful? Let other Firefox users know by voting next to the answer".

Now THIS is what Mozilla thinks is a 'solution'!!! The original QUESTION!!! WTF goes on in the heads of the morons who send these dumb emails?? They can't have even READ what they're actually sending!

I have now spoken on the phone, at great length, with Yahoo tech, and they INSIST this issue is nothing to do with them, but Thunbirbird, and repeatedly suggest I get in contact with them/Mozilla. This issue did happen earlier this year, around March, as was soon fixed with an updated Thundirbird, so why haven't TB/Moz fixed it again??

What lends this argument in Yahoos favor of it being a TB issue, is that if, as some say, that it's Yahoos decision to not allow mail to be sent ONLY to Bcc recipients, then why, when one sends mail using webmail on the actual Yahoo site, can one send to multiple Bcc recipients, without needing to add a single 'To' recipient into the list? Seems to point to a TBird issue to me.

Matt said

Yes the problem is yahoo. You are sending mail without anyone in the To:. YAhoo have made a unilateral decision that that is bad and reject mail that is exclusively send to BCC addresses.

Hi Matt, I don't know if you've read my post, below, but if one doesn't use an email client, in our case TB, but one goes to the Yahoo site to use webmail, then one CAN send to recipients using ONLY Bcc, without needing to put a single 'To' recipient in the mail. This to me gives strength to Yahoos argument that the fault lies with Mozilla/Thundirbird (as it's happened before). If Yahoo had made a unilateral decision, as you say, to stop exclusive Bcc mail, then we wouldn't be allowed to send mail this way from their own site either.

I'm still blaming Moz/TB, for that reason.

The topic here is yahoo, and their unilateral decision to not allow messages sent only to BCC recipients sent from mail clients. it has nothing to do with Thunderbird at all. Comparing what happens with Yahoo web mail and a mail client is a bit like comparing the Chicago Tribune the the New York Times. Both give you the news, but about there the similarities end.

As you appear enamored with incredimail, read what they says about the message. https://support.incredimail.com/hc/en-us/articles/230698447-Common-Send-Receive-Error-Messages

I draw your attention to the part where it says

These messages are usually not from IncrediMail; they are from your Email Server, or the Recipient's Email Server, and will give you a clue as to why they message was not sent.

Incredimail are saying it is a provider issue. I am saying it is a provider issue and the original post in the thread you got the email from decided it was a yahoo issue. https://support.mozilla.org/en-US/questions/1268916#answer-1254204

So if you are going to spend time on the phone with yahoo (I did not even know they had a phone) ask them exactly why their server is sending that message, instead of listening to rubbish about how their web interface is not affected. That is something I was already aware of. Just as I am aware there is no "Bulk mail" folder on the Yahoo web site, but there is one in their IMAP implementation. Using the logic your suggesting, Thunderbird must invent that folder full of Yahoo spam as well.

WOW - who got up on the wrong side of the bed this morning?? Where on Earth do you get the idea that I'm 'enamoured with Incredimail' Mark? Very weird thing to say.

6.6.0: The mail server that is the yahoo server who sent that message. The Yahoo smtp server is objecting to something in the email and blocking it.

Are you sending emails as a mailing list or several email address and you have only used Bcc for every recipient ? If the answer is yes: It has become a typical move by spammers who send out lists and use Bcc. Server are becoming more interested in stopping spammers. As a result Yahoo have chosen to block your emails because the spam detecting software scans emails as they are received by smtp server. This has nothing to do with Mozilla nor Thunderbird. Yahoo 's stance on this means it has become necessary to include at least one email address in a TO field, even if this is your own email address.

It may still be possible to send via webmail because it is not incoming to the smtp server and so Yahoo do not apply the same rules.

554: You'll receive an SMTP error or failed delivery message that includes "554 Message not allowed" when the content of a message you're trying to send violates Yahoo Mail policies. https://help.yahoo.com/kb/SLN5067.html

re : If Yahoo had made a unilateral decision, as you say, to stop exclusive Bcc mail, then we wouldn't be allowed to send mail this way from their own site either. You cannot compare because in webmail the emails are created within Yahoo and sent onwards.

An email client has to send emails from ouside of yahoo to yahoo via smtp server, this scans incoming mail that they need to send on to another server for delivery.

You are not being accepted by yahoo because they apply different rules depending upon how emails move through their servers.

You might say the methods to get through the servers are a workaround, but if yahoo set the rules and adding a TO field gets around Yahoo rules then that is what you need to do.

The content above should explain:

• what the error code mean
• why you got the error codes
• how to adjust your email to work with the Yahoo smtp server and spam rules.

Thanks 'Toad', that makes more sense to me. I've started doing as you say, and putting one 'To' recipient at the end of the Bcc list, which works, then I just have to delete the mail I recieve. Rgds