If you are sending to the same account, Microsoft drop the BCC as they assume it is an accident. Try BCCing your self to a different account.

Hi Matt, thank you for your reply. It looks like it is not a matter of Bcc'ing myself but everyone. After your answer I did many other tests and it looks like the BCC doesn't work at all using Tunderbird with Hotmail. i.e.: If I Bcc a friend he doesn't get the mail, instead if I compose and send the same message from the WEB or from my iPhone it works just fine. Moreover using Thunderbird with my Gmail account the Bcc works fine (either to myself or to my friend). I suppose there is an issue between the new release of Thunderbird and the new Hotmail (or Outlook, if you prefer) just updated few days ago. Could you have a try yourself? Should you need more details just ask, please. Thank you!

I tested in both 45.1.0 and 45.1.1 and what I see is as follows:

When I compose a message in my Hotmail account with a BCC, the "Sent" folder shows a message with the BCC, and then immediately after that a message without the BCC. The BCC recipient does not get the message.

I tried turning on logging. The third message shows up in the opposite order in the Hotmail Sent folder in Thunderbird, but in the same order online on Outlook.com (first the one with the BCC, then the one without).

I'm not sure how to read all of this, but it looks normal from Thunderbird's end:

19:19:22.380: SMTP Send: MAIL FROM:<username@hotmail.com> BODY=8BITMIME SIZE=2731 19:19:23.035: SMTP entering state: 0 19:19:23.035: SMTP Response: 250 2.1.0 username@hotmail.com....Sender OK 19:19:23.035: SMTP entering state: 5 19:19:23.035: SMTP Send: RCPT TO:<bcc_addressee> 19:19:23.351: SMTP entering state: 0 19:19:23.351: SMTP Response: 250 2.1.5 bcc_addressee 19:19:23.351: SMTP entering state: 6 19:19:23.351: SMTP entering state: 5 19:19:23.351: SMTP Send: RCPT TO:<to_addressee> 19:19:23.436: SMTP entering state: 0 19:19:23.436: SMTP Response: 250 2.1.5 to_addressee 19:19:23.436: SMTP entering state: 6 19:19:23.436: SMTP Send: DATA 19:19:23.733: SMTP entering state: 0 19:19:23.733: SMTP Response: 354 Start mail input; end with <CRLF>.<CRLF> 19:19:23.733: SMTP entering state: 7 19:19:23.734: SMTP entering state: 8 19:19:23.735: SMTP Send: . 19:19:26.240: SMTP entering state: 0 19:19:26.240: SMTP Response: 250 2.6.0 <message_id@hotmail.com> Queued mail for delivery 19:19:26.240: SMTP entering state: 9 19:19:26.240: SMTP Send: QUIT

An Outlook 2010 user reported having the same problem this month:

http://answers.microsoft.com/en-us/office/forum/office_2010-outlook/mails-sent-from-microsoft-outlook-using-hotmail/0d066e07-b13b-44b5-b9be-0b8c22c9c25b

I see you have a thread on MozillaZine (V45 impossible to send mailing list as BCC - mozillaZine Forums) where users report mixed results.

It's odd that different users have different experiences. In case it matters, the log shows this info for the server:

SMTP Response: 220 BLU436-SMTP248.smtp.hotmail.com Microsoft ESMTP MAIL Service, Version: 8.0.9200.16384 ready at Sun, 12 Jun 2016 12:19:21 -0700

My SMTP settings were created automatically when Thunderbird set up this account:

Server: smtp-mail.outlook.com Port: 587 Security: STARTTLS Auth method: Normal password

I don't see any options in the online mailbox related to BCCs.

I see... so I have posted a support request with Microsoft

I really do not expect anything from them as their track record of actually providing useful answers about email in their support forum is close to Zero. But I will try it.

Most of their support people do not know the difference between SMTP/POP and IMAP. That makes anything useful very hard to glean.

Thanks Matt, I voted as "Me Too" in both Microsoft pages (http://answers.microsoft.com/en-us/outlook_com/forum/oemail-oapps/bcc-on-mail-sent-via-smtp-using-outlookcom/d8a976e4-f50a-41c6-9f2b-b1cc204c2be4?tm=1465779105802 and http://answers.microsoft.com/en-us/outlook_com/forum/opeople-ocontacts/outlookcom-moving-addresses-from-bcc-field-to-the/b4505d03-7b66-4f98-a878-f1d82fcf42a6). Hope microsoft will fix this soon.

If you have your Hotmail account set up as an IMAP account, the messages you send from Thunderbird should show up in your Sent folder under the account, without having to BCC yourself. That doesn't solve the BCC problem for blind copying other people, but since you mentioned BCC'ing yourself originally, I thought I would note it.

Thanks jscher2000, I know that but I Bcc'ed my self in each message to verify if they were correctly sent. But now the issue is worst as we discovered that other people in Bcc are also not receiving the message

Hi Matt, checking the question you opened there are no valid answers from Microsoft as of yet. Have you found any further solution or do we have to wait for their reply? Thanks!

Piek said

Hi Matt, checking the question you opened there are no valid answers from Microsoft as of yet. Have you found any further solution or do we have to wait for their reply? Thanks!

Thunderbird can only do what it can do. It can not change the configuration of Microsoft's servers

I strongly suggest you change mail providers. GMX are good. I think better than Yahoo and AOL and Gmail is starting to get to corporate.

I'm not intended to change mail provider because I have so many accounts and contacts using my current e-mail address. Just wondering if Microsoft will fix the issue after your complain. I cannot believe I'm the only one having this issue with Bcc.

I have this problem, too. More than a nuisance.

I have a problem after the latest Thunderbird update 45.1.1, the recipients of Bcc to NOT get the email sent. You could list the email addresses to be sent in the Bcc line and in the to: field I always put UNDISCLOSED RECIPIENTS with the email address. But I do get the email in the TO: field (UNDISCLOSED RECIPIENTS info@xxxxxxxx.com), I’m really puzzled since it was working fine before?

Hi signtech, I don't think this is related to the last update, since I had this problem in Thunderbird 45.1.0 as well. It looks like a change in how Outlook.com works with mail programs that connect using IMAP/SMTP. I suspect no one has found a workaround yet.

I don't know if this helps (or not), but by using my "Gmail Account… within Thunderbird" I can send Bcc's & they are received as such by others. I still cannot use my Outlook Account within Thunderbird to send Bcc's. These are not received by others. I suspect the inability to send Bcc's via my Thunderbird Outlook Account may have coincided with an update of outlook.com. All this makes me suspect that the problem is in Outlook, not Thunderbird.

I do not know how much clearer I have to be.

Outlook have turned off the function for mail clients that do not use Microsoft's proprietary activsync technology. MY attempts to find out why have fallen on deaf ears at Outlook.com. As they are not interested in explaining why they took the action, I suggest there is little hope of changing the decision. However you all should be complaining on the outlook.com support site, not here. at least there your voices will be somewhere Microsoft might hear them.

There is absolutely nothing anyone associated with Thunderbird can do to make Microsoft stick to the rules and allow BCC mail. There will be no work around. Using another service to send your mail is all well and good, as long as that service agrees and the recipients actually get the mail without it being marked as spam. After all a good indicator of a spam message is one that claims to be from a site other than the one sending it.

As I indicated before, as Microsoft Customers you might stand a chance asking on their support site, but continued discussion on this forum will achieve nothing.

I have now been advised by Microsoft that they have rolled out a fix to about 75% of their servers and the rest should be patched within the week. So BCC should start working again.

If you still have issues after a week please speak up as they are of the opinion they have fixed this issue.

I have finally made contact with a human at Microsoft that we can discuss these sorts of issues with, so perhaps we can fix this and a couple of other issues.

Hi Matt,

this is a great news, it works to me now! I really thank you for your help and support here.

Cheers!