SymptomsI plan to switch from Qmail to Postfix or vice versa in Parallels Plesk Panel.
Will my EMail messages or queue be lost during the switching?
ResolutionEMail messages are not deleted during MTA switching. Old messages are available in Webmail.
Both Qmail and Postfix use same root directory PLESK_MAILNAMES_D to store incoming messages. For example email messages that come to MAIL@DOMAIN.TLD are stored in directory
Use the following article to get value of PLESK_MAILNAMES_D for your system: http://kb.sp.parallels.com/en/952
However mail queue is removed during MTA switching. It is recommended to process the queue before switching MTA.
Find details about how to switch MTA in Parallels Plesk Panel in this article: http://kb.sp.parallels.com/en/5801