Freescout: Error fetching emails: "Invalid mailbox list"

[taoeffect]

Running version 1.1.2, today everything seemed to be working fine but all of a sudden FreeScout can no longer fetch emails, and outputs this error when it tries:

[2018-12-14 20:40:04] Mailbox: <Mailbox name>
[2018-12-14 20:40:04] Folder: INBOX
[2018-12-14 20:40:04] Error: Invalid mailbox list: <>; File: /var/www/freescout.git/app/Console/Commands/FetchEmails.php (150)
[2018-12-14 20:40:04] Fetching finished

It seems to have been caused by a failed delivery email in the Inbox, likely because either the Return-path or To header was set to <> (my guess). Here are the headers of that email:

Return-Path: <>
Delivered-To: [email protected]
Received: from mail.website.com ([127.0.0.1])
  by mail.website.com with LMTP id GDr1DfKAFFx5JAAAXRy+/A
  for <[email protected]>; Fri, 14 Dec 2018 20:20:02 -0800
Received: (Haraka 30047 invoked for bounce); Fri, 14 Dec 2018 20:20:02 -0800
Date: Fri, 14 Dec 2018 20:20:02 -0800
From: [email protected]
To: <>
Subject: failure notice
Message-Id: <[email protected]>
Content-Type: multipart/report; report-type=delivery-status;
    boundary="boundary_3D69C48A-D84E-4182-B200-681FC991DEC5"
References: <[email protected]>
DKIM-Signature: v=1;a=rsa-sha256;bh=GW35JtOWUDUuTCUQWpUc3MU3aqrouc42wzNIIWGVl3s=;c=relaxed/simple;d=turtlemailbox.com;h=from:subject:date:message-id:to;s=s20181123173;b=q6nUGzOrQIDILD3xyCWxP3ZdniUnvEX9BINZQ6sP6gdftkloYLeyLjy6Aq7yO+M2ngIigNP5P7snHTDCAePiGYrRXA2kbhkXvuI88z1j6JIhOBqKrcifWELeB5ppRusVtR0dvg5AkdrCiM8PNqYdLdFu81PfK2wx1E6nXOJMPIabEcAwbeNgvH/psrAcxne58eYAMCzvhBex9hSHm6xVIDSxO7qQSOvlXgNpmQRGqToNnxRA5Niwoh7UpCXy0UeH2Mmqz3JZHSQ+UG4ai9VpsB9MlbMgrpyS+GMK2utPAoeuqgVCfLmQpWcWXPkyEMqNjvNLk93xO5rGlN0SMgUutA==

This is a MIME-encapsulated message.

[ ... rest of email continues ... ]

I managed to fix the problem by moving this email out of the INBOX and then clicking the "Clear Cache" button in the FreeScout system tools.

[freescout-helpdesk]

Similar issue https://github.com/glpi-project/glpi/issues/337
They concluded that it was IMAP problem of the mail server.

[taoeffect]

I do not understand French, however I do not think this has anything to do with IMAP. Accessing the IMAP server works just fine. Also, I do not see the same error they're getting in any php logs. I do not see this error either.

The problem started when this email appeared in the INBOX, and disappeared when I moved it out of the INBOX and cleared the cache. So I'm 99.9999999% certain the problem is with the email headers and not with IMAP.

[freescout-helpdesk]

Error message you got Invalid mailbox list is not present in the app or in the IMAP library https://github.com/Webklex/laravel-imap, which means it has been returned by your IMAP server. Apparently IMAP got broken because of this email and got fixed after you removed the email.

[taoeffect]

Hmm. That is odd. So it sounds like it's not a problem with FreeScout then but either with the server or with php-imap module. I will close this issue for now then. Thanks for your help.

[psuet]

I verified that every mail containing an empty Mail-Header, ie:

From: <>
Reply-To: <>

breaks FreeScout.

[freescout-helpdesk]

@psuet what error message are you getting in logs?

[psuet]

Same as above

Error: Invalid mailbox list: <>; File: /var/www/ticket/app/Console/Commands/FetchEmails.php (155)

I only wanted to document somewhere that not only To or Return-Path shows this behaviour. (still perfectly valid mails)

[freescout-helpdesk]

It will be fixed in the next release: https://github.com/freescout-helpdesk/freescout/commit/53ba824106f847cceae04165f2ccf1f26722798b

[taoeffect]

Dear @freescout-helpdesk — https://youtu.be/wmzyYquMS2I?t=59