When setting up a new IMAP account on Outlook 2016, I keep receiving an pop-up "An unknown error occurred, error code: 0x8004011c"
And if I used the wizard, "Something went wrong and Outlook couldn't set up your account." error will pop up. The "something went wrong..." error also appears when setting up an Exchange Online or Office365 account, so fix below is applicable.
Computer is joined to a local domain, and email is on Zarafa Server. IMAP is also enabled for this user account.

Solution:

On HKEY_LOCAL_MACHINE\Software\Microsoft\Cryptography\Protect\Providers\df9d8cd0-1501-11d1-8c7a-00c04fc297eb,

create or set a new registry DWORD value, named ProtectionPolicy, set the value 1

When setting up new POP account on Outlook 2016, testing it makes sending and receiving shows the error 0x80004005.
Computer is joined to a local domain, and email being setup is a POP account provided by a different mail hosting server.



Solution: On HKEY_LOCAL_MACHINE\Software\Microsoft\Cryptography\Protect\Providers\df9d8cd0-1501-11d1-8c7a-00c04fc297eb,

create or set a new registry DWORD value, named ProtectionPolicy, set the value 1

Disabling notification (receiving email) didn't work.

Zarafa-webaccess attachment disappeared when I reply to an email but no to a New email. Zarafa version installed is WebApp 1.6-46049, ZCP 7.1.14-51822.

Attachment will not show up at the receiver's Inbox and in my Sent Items.

I tried using Firefox and Chrome and had the same result.

Solution: Increase the MaxExecutionTime, MemoryLimit, PostMaxSize on PHP server where you have the Zarafa server installed.

On SME Server Contribs, you do it by issuing the following commands:

db configuration setprop php MaxExecutionTime 4800 
db configuration setprop php MemoryLimit 250M 
db configuration setprop php PostMaxSize 40M 
expand-template /etc/php.ini 
/etc/init.d/httpd-e-smith restart

Update Nov 2016:
We are still having issues with the attachment but it's intermittent, this time I updated the WebApp to the latest version compatible to the server's OS.

Scenario: We have an Exchange Server 2007 (itropics.net) in house. When our supplier (supplier.com) sent us an email, they receive a bounced back error message: mail.itropics.net #554 5.1.0 Sender denied

To fix that, make sure that the supplier's domain named is not being blocklisted by your Exchange Server. Go to Exchange Management Console -> Organization Configuration -> Hub Transport -> Anti-spam -> Sender Filtering and make sure that the supplier domain name is not on the list. Remove it if it's there.

Or check the recipient's (user@itropics.net) Blocked Senders to see if the domain is in the list. You can do it by checking Outlook (go to Tools menu then Junk E-mail Protection) or logging into OWA

1. Login to Google Admin Console and make sure the POP is enabled on all email accounts you want to setup on SBS POP3 Connector.
   
   
   Add a comment

1. Uninstall the anti-virus
2. Backup the *.dbx file
3. Working offline (File -> tick Work Offline)
4. Perform a manual compact (File -> Folder -> Compact)
5. Close Outlook Express
6. Find and Rename “outbox.dbx”, ”sent.dbx”, “folder.dbx”…….. Open CMD, then type dir *.dbx /s to find the exact location of the file.
7. Try to open OE and send email again. It should regenerate new “outbox.dbx”, ”sent.dbx”, “folder.dbx”