This error will cripple Sugar’s email functionality, which is a major development in version 5.0, previous versions of SugarCRM Community Edition (free) did not handle emails at all. This error happens when the php5-imap extension hasn’t been installed. After searching for sometime I found a reference to php5-imap and decided to give it a try. Here is how you install it under Debian (ubuntu), very simple.
1- as root #apt-get install php5-imap (a blue screen will ask if you want to install it without maildir support – if all you need it for is SugarCRM click yes)
2 – restart Apache – #/etc/init.d/apache2 restart
See painless! For other distributions, just search for php imap on your Package Manager like Yast or Synaptic.