increase spampd maximum message size from 64KB to 500KB, matching the spamc default

see https://discourse.mailinabox.email/t/allow-spamassassin-to-scan-emails-larger-than-250kb/391

CHANGELOG.md

@@ -6,6 +6,7 @@ In Development
 
 Mail:
 
+* Spam checking is now performed on messages larger than the previous limit of 64KB.
 * POP3S is now enabled (port 995).
 * In order to guard against misconfiguration that can lead to domain control validation hijacking, email addresses that begin with admin, administrator, postmaster, hostmaster, and webmaster can no longer be used for (new) mail user accounts, and aliases for these addresses may direct mail only to the box's administrator(s).
 

setup/spamassassin.sh

@@ -25,10 +25,14 @@ tools/editconf.py /etc/default/spamassassin \
 # Configure pyzor.
 hide_output pyzor discover
 
-# Pass messages on to docevot on port 10026.
-# This is actually the default setting but we don't want to lose track of it.
-# We've already configured Dovecot to listen on this port.
-tools/editconf.py /etc/default/spampd DESTPORT=10026
+# Configure spampd:
+# * Pass messages on to docevot on port 10026. This is actually the default setting but we don't
+#   want to lose track of it. (We've configured Dovecot to listen on this port elsewhere.)
+# * Increase the maximum message size of scanned messages from the default of 64KB to 500KB, which
+#   is Spamassassin (spamc)'s own default. Specified in KBytes.
+tools/editconf.py /etc/default/spampd \
+	DESTPORT=10026 \
+	ADDOPTS="\"--maxsize=500\""
 
 # Spamassassin normally wraps spam as an attachment inside a fresh
 # email with a report about the message. This also protects the user