nopaste

my $client = Fastmail::Client->....;

my $mbox_res = $client->request([
  [ 'Mailbox/get', { accountId => ... } ],
]);

# Get all the mailbox objects:
my @boxes = $mbox_res->single_sentence('Mailbox/get')->arguments->{list}->@*;

my ($newsletter) = grep {; $_->{name} eq 'Newsletters' } @boxes;

die "WTF?!" unless $newsletter;

# NOTE: this will only find *direct* children; finding deep ancestors is left
# as an exercise for the reader (or, like, don't do that)
my @boxes_of_interest = grep {; $_->{parentId} eq $newsletter->{id} } @boxes;
exit unless @boxes_of_interest; # I guess we don't have any...

my $mail_res = $client->request([
  [
    'Email/query',
    {
      filter => {
        createdAfter => '30 days ago',
        also => {
          operator   => 'or',
          conditions => [
            map {; { mailboxId => $_->{id} } } @boxes_of_interest
          ],
        }
      }
    },
    'a',
  ],
  [
    'Email/get',
    {
      properties => [ ??? ],
      '#ids' => {
        resultOf => 'a',
        name => 'Email/query',
        path => '/ids',
      }
    },
  ],
]);

my @mail = $mail_res->sentence_named('Email/get')->arguments->{list}->@*;

# NEXT:
# group mail into groups by the mailboxes they're in
# sort them into rev. chron order or something
# build the XML::Feed objects
# write them out
# done!