AtMail webmail component was removed during upgrade from Plesk 10.4 to Plesk 11.5 via VZ templates.
Since pp11.5-webmail template package set was reduced, psa-atmail was removed. During installation of base template pp11.5 package plesk-web-hosting marks phpX-configurator version less than 1.6.3 as conflicted. As far as atmail requires in phpX-configurator it marked for uninstall also. Later package phpX-configurator is installed by non-template (packages) depends.
Specify php template
pp11.5-php5.3 during upgrade via vz templates, e.g.
# vzpkg install $VE_ID pp11.5-webmail pp11.5-panel-addons pp11.5-cf-support pp11.5-antivirus pp11.5 pp11.5-webhosting-addons pp11.5-migration pp11.5-qmail pp11.5-tomcat pp11.5-kav pp11.5-spamassassin pp11.5-mailman pp11.5-watchdog pp11.5-php5