rude answer... stop using gmail.

Gmail does not store BCC addresses so any imap account that synchronizes the sent folder will have to sent information retained.

Solution do not use Gmail for sent the send folder use local folders so it is not synchronized into oblivion.

Tools menu (alt+T) > Account settings > Copies and folders for the account and change sent to other and make it the local folder.

I don't use Gmail! I already have the recommended account setting. My problem is that there is no record of the recipients of Bcc emails that I send; simply a "undisclosed recipients" statement. In Eudora, which has been my email program, the full list of recipients regardless of "To" "Cc" or "Bcc" is provided in the To/Recipient column.

When sending to only Bcc adressees, the actual list is not shown in the recipients column.

Can you explain what 'recipients column' means?

You can see the actual recipients of the message when you open the copy of the sent message in the Sent folder. As Matt said, this apparently doesn't work with Gmail IMAP.

Thanks for that C1. My problem was that in the Recipients column in Local Folders (after I had transferred "Sent" emails), any Bcc only email I had sent showed only "undisclosed recipients". In Eudora, there would have been the entire list of Bcc adressees. I am now aware that to see who I sent a Bcc only email to I have to open the email. Simple really, but one more step than I have been used to.