%%%%%%%%%%@yahoo.com
%%%%%%@wanadoo.fr
%%%%raviplywoodglasscentre@yahoo.comravi
%%nameemail%%@yahoo.com
%.getincontact@numberland.com
%1%3@example.com
%1@example.com

yahoo.com,%%%%%%%%%%@yahoo.com
wanadoo.fr,%%%%%%@wanadoo.fr
yahoo.comravi,%%%%raviplywoodglasscentre@yahoo.comravi
yahoo.com,%%nameemail%%@yahoo.com
numberland.com,%.getincontact@numberland.com
example.com,%1%3@example.com
example.com,%1@example.com

yahoo.com,%%%%%%%%%%@yahoo.com,%%nameemail%%@yahoo.com
wanadoo.fr,%%%%%%@wanadoo.fr
yahoo.comravi,%%%%raviplywoodglasscentre@yahoo.comravi
numberland.com,%.getincontact@numberland.com
example.com,%1%3@example.com,%1@example.com

$ perl -F@ -alne '
    push @{ $h{$F[1]} }, $_ }{
    for $k (reverse sort keys %h) {print join ",", $k, @{ $h{$k} }
  }' emails.csv
yahoo.comravi,%%%%raviplywoodglasscentre@yahoo.comravi
yahoo.com,%%%%%%%%%%@yahoo.com,%%nameemail%%@yahoo.com
wanadoo.fr,%%%%%%@wanadoo.fr
numberland.com,%.getincontact@numberland.com
example.com,%1%3@example.com,%1@example.com

python3 /path/to/group_domains.py /directory/with/files

example.com,%1%3@example.com,%1@example.com
numberland.com,%.getincontact@numberland.com
wanadoo.fr,%%%%%%@wanadoo.fr
yahoo.com,%%%%%%%%%%@yahoo.com,%%nameemail%%@yahoo.com
yahoo.comravi,%%%%raviplywoodglasscentre@yahoo.comravi

lines.sort(key=itemgetter(1))

groupby(lines, itemgetter(1))

some_list.txt

grouped_some_list.txt

python3 /path/to/group_domains.py /directory/with/files

python3 /path/to/group_domains.py /directory/with/files /path/to/outputfile.txt

awk -F, '{a[$1] = a[$1]","$2} END {for (i in a) print i a[i]}'

$ awk -F, '{a[$1] = a[$1]","$2} END {for (i in a) print i a[i]}' foo
yahoo.comravi,%%%%raviplywoodglasscentre@yahoo.comravi
yahoo.com,%%%%%%%%%%@yahoo.com,%%nameemail%%@yahoo.com
numberland.com,%.getincontact@numberland.com
example.com,%1%3@example.com,%1@example.com
wanadoo.fr,%%%%%%@wanadoo.fr