when I try to implement other local delivery software for e.g. I need to modify .qmail file when a new email account is created/updated via plesk . if you just edit .qmail it will be rewrite on any email account update from plesk and same for new accounts you have to provision this shit somehow.
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Most questioned issue. how could we recompile plesk qmail with needed options and patches? If you wanna do it just check the bellow link:
http://kb.parallels.com/en/1161
all parallels patches provided from plesk 8.2 to plesk 9.0 , which by the way can finally use postfix