When Sieve is enabled, dovecot-lda is used to deliver mail in mailboxes (so it can apply sieve scripts) instead of qmail. Dovecot-lda is more ressources intensives than qmail, so you may have performance penalty when users receive a lot of mails (for example, when you use the Bcc qpsmtpd's plugin to copy every mail in one mailbox). You can selectivly disable dovecot-lda for some users, for example, to disable dovecot-lda for user maillog:
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When Sieve is enabled, [http://wiki2.dovecot.org/LDA dovecot-lda] is used to deliver mail in mailboxes (so it can apply sieve scripts) instead of qmail. Dovecot-lda is more ressources intensives than qmail, so you may have performance penalty when users receive a lot of mails (for example, when you use the Bcc qpsmtpd's plugin to copy every mail in one mailbox). You can selectivly disable dovecot-lda for some users, for example, to disable dovecot-lda for user maillog: