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So, if sieve is invoked by lda, then, probably, I could invoke dovecot-lda from wrapper script on each mail after it is fetched?

with getmail

[destination] type = MDA_external path = /usr/lib/dovecot/deliver

But then it will be copied to INBOX... -- Is it possible to specify the other folder to deliver to,

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to the deliver program?

the sieve filter invoked bx deliver does it, i.e rule

if header :contains ... fileinto :create "folder"

or whatever

Ah, yes. Really, I looked to mpop options, it can call various LDA's. And, dovecot-lda has "-m" parameter, which allows to specify the mailbox name. So, I can deliver the mail arrived by fetcher, via dovecot-lda, and Sieve filters will work. Also, as a bonus, delivering mail via LDA will correctly update user quotas -- the problem which resolved by itself :) Great :)

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outgoing mail to folders, specific

outgoing mail is smtp, with i.e imap copy to sent folder etc if you want other folders your imap client should do it

So, I can invoke Sieve interpreter from SMTP server, or process it via dovecot-lda, like in fetcher case?

in general ,i dont think so , there may be some workaround with server bcc_copy and i.e plus adressing with sieve then for "sent" mail

Yes, this is a variant. But what if I modify the Dovecot post-login script (a wrapper for IMAP process), or add the sieve plugin to protocol "imap {mail_plugins = ...}" ? Will it be invoked on each operation with mailboxes?

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try i.e

https://addons.mozilla.org/de/thunderbird/addon/send-filter/?src=search

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to their recipients.

WBR, valery