Hi, After some tests, it appears that a single X-Debbugs-CC header must be used, otherwise the last one is the one that prevails. This matches my reading of the 'process' script of the GNU Debbugs instance [0], and thus must conform to the same email rules outlined in RFC5322 for the To or CC fields (only one such header must be used); multiple values can be separated by a comma. [1]
--8<---------------cut here---------------start------------->8--- my %header; for my $hdr (@headerlines) { $hdr = decode_rfc1522($hdr); $_ = $hdr; s/\n\s/ /g; &finish if m/^x-loop: (\S+)$/i && $1 eq "$gMaintainerEmail"; my $ins = !m/^subject:/i && !m/^reply-to:/i && !m/^return-path:/i && !m/^From / && !m/^X-Debbugs-/i && !m/^cc:/i && !m/^to:/i; $fwd .= $hdr."\n" if $ins; # print DEBUG ">$_<\n"; if (s/^(\S+):\s*//) { my $v = lc $1; print DEBUG ">$v=$_<\n"; ## There may be multiple To: or Cc: headers (see bug#5996). if ( ($v eq 'to' || $v eq 'cc') && defined $header{$v} && length($header{$v}) ) { $header{$v} = $header{$v} . ', ' . $_ if length($_); } else { $header{$v} = $_; } } else { print DEBUG "!>$_<\n"; } } $header{'message-id'} = '' if not defined $header{'message-id'}; --8<---------------cut here---------------end--------------->8--- Only 'to' or 'cc' multiple headers are coalesced into one; otherwise the $header specific key (for a given header) is overridden to the last value encountered at line '$header{$v} = $_;', IIUC. Our teams.scm script should be adjusted to produce a single X-Debbugs-CC header with comma-separated values. [0] https://gitlab.com/npostavs/debbugs/-/blob/gnu-reconstruction/scripts/process#L171 [1] https://datatracker.ietf.org/doc/rfc5322/, 3.6 Field Definitions -- Thanks, Maxim