commit a8ccdaf109b85cedfd609678d95f7b7d5fdb91f5

Author: ellie timoney <ellie@fastmail.com>

Date:   Mon Jun 7 12:00:27 2021 +1000

    lmtpd: shared mailboxes don't have conversations to lock

    Fixes #3488

diff --git a/imap/lmtpd.c b/imap/lmtpd.c

index 498bb8765..dc9ca21bc 100644

--- a/imap/lmtpd.c

+++ b/imap/lmtpd.c

@@ -843,8 +843,10 @@ int deliver(message_data_t *msgdata, char *authuser,

             // lock conversations for the duration of delivery, so nothing else can read

             // the state of any mailbox while the delivery is half done

             struct conversations_state *state = NULL;

-            r = conversations_open_user(mbname_userid(mbname), 0/*shared*/, &state);

-            if (r) goto setstatus;

+            if (mbname_userid(mbname)) {

+                r = conversations_open_user(mbname_userid(mbname), 0/*shared*/, &state);

+                if (r) goto setstatus;

+            }

             /* local mailbox */

             mydata.cur_rcpt = n;