IMAP protocol support in mail servers on Plesk for Windows
Parallels Plesk Panel for Windows is supplied with MailEnable Standard Edition mail server by default. MailEnable Standard supports IMAP since Plesk 10.x, however IMAP support was not available in earlier versions and upgrade to MailEnable Professional, Enterprise or Premium was necessary see feature comparison table on MailEnable website.
SmarterMail Lite edition does not support IMAP see documentaion.
Other mail servers, supported by Parallels Plesk Panel, have built-in support for IMAP protocol which is enabled by default. Mailboxes can be accessed from any IMAP-compatible mail client through port 143 or 993 (IMAP-over-SSL).
List of supported mail servers and their respective versions can be found in product release notes: