When running current master on Debian stable if I invoke:

   b4 am -P 59 c0efb81064f71837f19408f65b52d155103ee514.1605896059.git.gustavoars@kernel.org 

I get the traceback below unless I remove python3-dkim:

Looking up https://lore.kernel.org/r/c0efb81064f71837f19408f65b52d155103ee514.1605896059.git.gustavoars%40kernel.org
Grabbing thread from lore.kernel.org/linux-hardening
Analyzing 212 messages in the thread
---
Writing ./20201120_gustavoars_fix_fall_through_warnings_for_clang.mbx
Traceback (most recent call last):
  File "/home/broonie/git/b4/b4/command.py", line 220, in <module>
    cmd()
  File "/home/broonie/git/b4/b4/command.py", line 203, in cmd
    cmdargs.func(cmdargs)
  File "/home/broonie/git/b4/b4/command.py", line 40, in cmd_am
    b4.mbox.main(cmdargs)
  File "/home/broonie/git/b4/b4/mbox.py", line 511, in main
    mbox_to_am(threadmbox, cmdargs)
  File "/home/broonie/git/b4/b4/mbox.py", line 117, in mbox_to_am
    linkmask=config['linkmask'], cherrypick=cherrypick)
  File "/home/broonie/git/b4/b4/__init__.py", line 532, in save_am_mbox
    if latt and latt.validate(lmsg.msg):
  File "/home/broonie/git/b4/b4/__init__.py", line 1812, in validate
    self.lsig = LoreAttestationSignatureDKIM(msg)
  File "/home/broonie/git/b4/b4/__init__.py", line 1639, in __init__
    if not dkim.verify(self.msg.as_bytes(), dnsfunc=dkim_get_txt):
  File "/usr/lib/python3/dist-packages/dkim/__init__.py", line 1291, in verify
    return d.verify(dnsfunc=dnsfunc)
  File "/usr/lib/python3/dist-packages/dkim/__init__.py", line 888, in verify
    return self.verify_sig(sig, include_headers, sigheaders[idx], dnsfunc)
  File "/usr/lib/python3/dist-packages/dkim/__init__.py", line 677, in verify_sig
    pk, self.keysize, ktag = load_pk_from_dns(name, dnsfunc)
  File "/usr/lib/python3/dist-packages/dkim/__init__.py", line 423, in load_pk_from_dns
    s = dnsfunc(name)
  File "/home/broonie/git/b4/b4/__init__.py", line 2347, in dkim_get_txt
    a = _resolver.resolve(lookup, dns.rdatatype.TXT, raise_on_no_answer=False, lifetime=timeout, search=True)
AttributeError: 'Resolver' object has no attribute 'resolve'