Locate path in your project:
vendor/uvdesk/mailbox-component/Console/RefreshMailboxCommand.php
Open RefreshMailboxCommand.php and make changes here as suggested below.
$imap = imap_open("{xx.xx.xx.xx:993/imap/ssl/novalidate-cert}", 'mydomain/user', 'password', NULL, 1, array('DISABLE_AUTHENTICATOR' => 'GSSAPI'));
Hope it will help to resolve for Exchange server !!