What email programs do? (webmail does not count) Is it from the same outgoing account account? What mail provider are you using? Do all recipients not getting BCC have addresses on the same domain?

Because this problem coincided with a new version of Thunderbird and using bcc worked fine before this change, I was hoping for an answer from you. I send out an email using a local internet service provider's email to recipients at addresses of many (maybe 20) different domains. A friend of mine who uses Thunderbird found the same problem at the same, and he uses a different internet program. So I believe the problem is not with my email or the recipients' various email servers. At this point I don't see any option to but to give up on Thunderbird, which until this problem, I liked very much.

re : weekly email with a bcc list of about 50 recipients

Are you using a 'Mailing List' ? Or do you add each email address independently?

Do you use 'Mail Merge' addon ? Do you use 'MRC compose' addon ? Does this occur if you use Thunderbird in Safe Mode? Help > Restart with addons disabled.

Test: Does it occur if send one email to a friend or other personal email address and include your email address in a Bcc.

No I'm not using a Mailing List. No I do not use Mail Merge or MRC compose add ons. I haven't tried using Thunderbird in Safe Mode. As I said, it worked fine prior to the last Thunderbird update. I have made numerous tests sending emails to myself. When I put one of my email addresses in a Bcc, and another in the "To" recipient, regardless of which email addresses I use, I never get the Bcc copy but always get the "To" email.

What mail provider are you using? BT, gmail, comcast, bigpond etc?

I use two - a local ISP (Digis, Idaho) that has an email server and also a web based email, MSN Outlook.

You do not mention that anything is being bounced back, so I'm wondering if you have triggered the server's spam filters.

Suggest you try: Create a Mailing List and use the method option of sending from the Write window. Put your name in the TO field and use the 'Addto Bcc' to insert the Mailing List. then see how many receive emails.

• https://support.mozilla.org/en-US/kb/how-create-and-use-mailing-lists-thunderbird

Second option would be to use the 'Mail Merge' addon. This would allow you to send more personalised emails. So each person/contact would be sent an individual email in a TO field, but you only compose one email. download and install this addon:

• https://addons.mozilla.org/en-US/thunderbird/addon/mail-merge/?src=hp-dl-featured

Create an address book or Mailing list that only has people you want to send to. Export that address book or Mailing list as a .csv file and save somewhere you can locate easily.

Create a Template email as per instructions on addon website. I've included some images to assist. I put Mail Merge in Subject, but you can put whatever you like, remember it is used to identify the template folder and when you compose the email, you can always edit it. Save as Template.

Instructions on setting it up are located on the addon webpage under this heading: Step by Step: (CSV) When setting up the sending option, I use 'Send Later' as this puts all emails in my Outbox, just so I can double check it has worked ok.

Once this method has been set up, it is very efficient and easy to use.

Thanks for your suggestions. I created a mailing list. How exactly do I correctly insert the mailing list into the Bcc line? I can select it from the address book or start typing the mailing list name and it recognizes it, but then when I send the message I get the following error: the "(name I gave the mailing list) is not a valid e-mail address because it is not of the form user@host. You must correct it before sending the e-mail." Where exactly do I find the "add to bcc" function?

I just found the "add to bcc" button in the contacts list and tried inserting the list that way. But the result was the same when I tried to send the note; I got the same error message.

ok, I think I found the problem. The name I gave the mailing list had a un-allowed character. I changed the name of an abbreviated mailing list and I think it worked. So thanks for your help