Sending with bcc fails

[mooomooo]

Trying to send an email from neomutt with a bcc: recipient, it fails with the following error:

Traceback (most recent call last):
  File "/usr/bin/gmi", line 24, in <module>
    g.main ()
  File "/usr/lib/python3.12/site-packages/lieer/gmailieer.py", line 418, in main
    args.func(args)
  File "/usr/lib/python3.12/site-packages/lieer/gmailieer.py", line 1048, in send
    raise ValueError(
ValueError: Recipients passed via sendmail(1) arguments, but not part of message headers: testbcc@example.com

lieer v1.6 installed via pip on alpine 3.21.3; NeoMutt 20241114