Out of interest, who is the email provider?

The "undisclosed recipients:" is put there by Thunderbird, and would not, I hope, be affected by the choice of email provider. But some providers do aggressive things to Bcc addresses.

Allegedly, the "undisclosed recipients:" is inserted because a few email servers assume that an empty To or Cc field indicates spam or worse, so it would not be good if this has gone missing.

My email provider is Charter. I have used TB through charter for 15 years with out this issue. I use POP, all files are stored on this system hard drive. Only when I updated to 45.4 did this occur. Also of note: As of my update to 45.4, all SENT email from every account from 15 years to present suddenly have in the recipient column "undisclosed recipient" missing, it's now blank. How could my provider get into my file system and alter 15 years of stored emails to alter the recipient data?

Thank you for looking into this issue Mike H

Are you the same Mike H who posted on the newsgroup?

Dňa 17.11.2016 o 18:50 Mike H napísal(a):

Just updated to TB45.4 and noticed that in all of my SENT folders the RECIPIENT space is blank ONLY for email sent using only BCC. The RECIPIENT space had "UNDISCLOSED RECIPIENT" before I updated. Is there a fix, is this a bug, was this feature removed, is there a config setting?

Thank you for your time and consideration

Mike H

Check the value of the preference mail.compose.add_undisclosed_recipients via tools->options->advanced->config editor

Does that advice work out for you?

That value is "TRUE". I have tried true and false, no joy