According to the Dovecot mailing list, in version 1.2 of Dovecot login_greeting_capability was removed and is no longer needed.
I'm assuming it is erroring out because you are running v1.2 or newer.
Here's two quotes I found regarding this configuration setting:
1.
details: http://hg.dovecot.org/dovecot-1.2/rev/6d1214687c89
changeset: 7944:6d1214687c89
user: Timo Sirainen
date: Sun Jun 22 07:12:27 2008 +0300
description:
Removed login_greeting_capability setting, it's no longer used.
diffstat:
1 file changed, 5 deletions(-)
dovecot-example.conf | 5 -----
diffs (15 lines):
diff -r 138a64b6dffe -r 6d1214687c89 dovecot-example.conf
--- a/dovecot-example.conf Sat Jun 21 18:19:41 2008 +0300
+++ b/dovecot-example.conf Sun Jun 22 07:12:27 2008 +0300
@@ -536,11 +536,6 @@ protocol imap {
list of plugins to load.
mail_plugins =
mail_plugin_dir = /usr/lib/dovecot/imap
Send IMAP capabilities in greeting message. This makes it unnecessary for
clients to request it with CAPABILITY command, so it saves one round-trip.
Many clients however don't understand it and ask the CAPABILITY anyway.
login_greeting_capability = no
IMAP logout format string:
%i - total number of bytes read from client
2.
"Removed login_greeting_capability. The capabilities are now always sent (Lemonade requires this and it's not that much extra traffic)."