When a user's mailbox is showing set in mailenable as well as in plesk but you still get an error during delivery try this

 **Just follow the step example is given below ** :-

- Goto %plesk_dir%/mailservers/mailenable/config

- Take a backup of ADDRESS-MAP.TAB

- Open ADDRESS-MAP.TAB in wordpad

You should see mailboxes in this format :-

[SMTP:abuse@securediscovery.com]   

[SF:securediscovery.com/harry]
     
 securediscovery.com    0

Each mailbox MUST be in one line,

if you see a line break eg;

[SMTP:abuse@securediscovery.com]  

 [SF:securedisry.com/harry]         

 securediscovery.com    0

Edit the text and make sure its in ONE line.Almost all the time, when a line breaks,
some characters are missing,so when you edit-make sure the there are no missing characters
in that line,This is very important and should be done carefully.

{Important}:-

Once this is done, restart mail-enable and test that mailbox.