1 files changed, 12 insertions, 0 deletions
diff --git a/lib/PublicInbox/Inbox.pm b/lib/PublicInbox/Inbox.pm
index a1e34797..da7ea75f 100644
--- a/lib/PublicInbox/Inbox.pm
+++ b/lib/PublicInbox/Inbox.pm
@@ -421,4 +421,16 @@ sub uidvalidity { $_[0]->{uidvalidity} //= eval { $_[0]->mm->created_at } }
  
  sub eidx_key { $_[0]->{newsgroup} // $_[0]->{inboxdir} }
  
+sub mailboxid { # rfc 8474, 8620, 8621
+        my ($self, $imap_slice) = @_;
+        my $pfx = defined($imap_slice) ? $self->{newsgroup} : $self->{name};
+        utf8::encode($pfx); # to octets
+        # RFC 8620, 1.2 recommends not starting with dash or digits
+        # "A good solution to these issues is to prefix every id with a single
+        #  alphabetical character."
+        'M'.join('', map { sprintf('%02x', ord) } split(//, $pfx)) .
+                (defined($imap_slice) ? sprintf('-%x', $imap_slice) : '') .
+                sprintf('-%x', uidvalidity($self) // 0)
+}
+
  1;