sieve compile error

[Johannes Rohr]

Dear all, I try to recompile my learn_ham.sieve script, which fails
with the message
root at ida:/etc/dovecot# sievec sieve-scripts/report-ham.sieve 
report-ham: line 1: error: require command: unknown Sieve capability
`vnd.dovecot.pipe'.report-ham: line 1: error: require command: unknown
Sieve capability `imapsieve'.report-ham: line 19: error: unknown
command 'pipe' (only reported once at first occurrence).report-ham:
error: validation failed.sievec(root): Fatal: failed to compile sieve
script 'sieve-scripts/report-ham.sieve'
Yes, in conf.d/20-imap.conf, imapsieve and vnd.dovecot.pipe are
explicitly enabled:
protocol imap {  mail_plugins = $mail_plugins imap_sieve imap_acl 
mail_max_userip_connections = 50
plugin {sieve_plugins = sieve_imapsieve sieve_extprograms  # From
elsewhere to Spam folder  imapsieve_mailbox1_name = Spam 
imapsieve_mailbox1_causes = COPY  imapsieve_mailbox1_before =
file:/etc/dovecot/sieve-scripts/report-spam.sieve  # From Spam folder
to elsewhere  imapsieve_mailbox2_name = *  imapsieve_mailbox2_from =
Spam  imapsieve_mailbox2_causes = COPY  imapsieve_mailbox2_before =
file:/etc/dovecot/sieve-scripts/report-ham.sieve#sieve_pipe_bin_dir =
/etc/dovecot/sieve-scriptssieve_global_extensions =
+vnd.dovecot.execute +vnd.dovecot.pipe
	}}

I am obviously overlooking something here, but what?
Any hints will be greatly appreciated!
Johannes
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