diff --git a/sarracenia/config/__init__.py b/sarracenia/config/__init__.py
index 2cd78536d..a3f4e01f7 100644
--- a/sarracenia/config/__init__.py
+++ b/sarracenia/config/__init__.py
@@ -114,7 +114,7 @@ def __repr__(self) -> str:
     'post_documentRoot': None,
     'post_baseDir': None,
     'post_baseUrl': None,
-    'post_format': 'v03',
+    'post_format': None,
     'realpathPost': False,
     'recursive' : True,
     'runStateThreshold_reject': 80,
diff --git a/sarracenia/config/publisher.py b/sarracenia/config/publisher.py
index 9c232155f..f52dfb2de 100644
--- a/sarracenia/config/publisher.py
+++ b/sarracenia/config/publisher.py
@@ -63,13 +63,17 @@ def __init__(self, options ):
         if hasattr(options,'tlsRigour') :
             self['tlsRigour'] = options.tlsRigour
     
-        if hasattr(options,'post_format') :
+        if hasattr(options, 'post_format') and options.post_format is not None:
             self['format'] = options.post_format
-        elif hasattr(options,'post_topicPrefix') and options.post_topicPrefix[0] in [ 'v02', 'v03' ]:
+        elif hasattr(options, 'post_topicPrefix') and options.post_topicPrefix \
+                and options.post_topicPrefix[0] in ['v02', 'v03']:
             self['format'] = options.post_topicPrefix[0]
         else:
             self['format'] = 'v03'
 
+        # exportAny and exportMine expect 'post_format' in the options dict
+        self['post_format'] = self['format']
+
         if hasattr(options,'post_topicPrefix') and options.post_topicPrefix:
             self['topicPrefix'] = options.post_topicPrefix
         elif hasattr(options, 'topicPrefix') and options.topicPrefix:
diff --git a/sarracenia/moth/__init__.py b/sarracenia/moth/__init__.py
index 37c1f8b09..e36907dfc 100644
--- a/sarracenia/moth/__init__.py
+++ b/sarracenia/moth/__init__.py
@@ -271,6 +271,8 @@ def pubFactory(props) -> 'Moth':
             props['broker'] = broker
             if 'exchange' in publisher:
                 props['exchange'] = publisher['exchange']
+            if 'format' in publisher:
+                props['format'] = publisher['format']
 
         elif not props['broker']:
             logger.error('no broker specified')
@@ -347,6 +349,8 @@ def __init__(self, props=None, is_subscriber=True) -> None:
                     self.o['exchange'] = publisher['exchange']
                 if 'topicPrefix' in publisher:
                     self.o['topicPrefix'] = publisher['topicPrefix']
+                if 'format' in publisher:
+                    self.o['format'] = publisher['format']
 
         # apply settings from props.
         if 'settings' in self.o:
diff --git a/tests/sarracenia/config/publisher_test.py b/tests/sarracenia/config/publisher_test.py
new file mode 100644
index 000000000..6d7b47b66
--- /dev/null
+++ b/tests/sarracenia/config/publisher_test.py
@@ -0,0 +1,105 @@
+import pytest
+from tests.conftest import *
+from unittest.mock import MagicMock
+
+from sarracenia.config.publisher import Publisher
+
+
+def make_options(**overrides):
+    """Minimal options object for Publisher."""
+    opts = MagicMock()
+    opts.post_broker = MagicMock()
+    opts.post_broker.url = MagicMock()
+    opts.post_broker.url.username = 'tsource'
+    opts.post_broker.url.scheme = 'amqp'
+    opts.post_exchange = ['xs_tsource']
+    opts.post_baseDir = '/tmp'
+    opts.post_baseUrl = 'http://localhost'
+    opts.post_exchangeSplit = 0
+
+    # defaults matching config/__init__.py
+    opts.post_format = None
+    opts.post_topicPrefix = ['v03', 'post']
+
+    for k, v in overrides.items():
+        setattr(opts, k, v)
+
+    return opts
+
+
+def test_format_defaults_to_v03():
+    """When neither post_format nor post_topicPrefix is set, default to v03."""
+    opts = make_options()
+    del opts.post_topicPrefix
+    del opts.post_format
+    pub = Publisher(opts)
+    assert pub['format'] == 'v03'
+    assert pub['post_format'] == 'v03'
+
+
+def test_format_derived_from_v02_topicprefix():
+    """post_topicPrefix v02.post should derive format v02.
+
+    This is the bug that Peter found -- post_format defaulted to 'v03'
+    which always took priority, so post_topicPrefix was never used.
+    """
+    opts = make_options(post_topicPrefix=['v02', 'post'])
+    pub = Publisher(opts)
+    assert pub['format'] == 'v02'
+    assert pub['post_format'] == 'v02'
+
+
+def test_format_derived_from_v03_topicprefix():
+    """post_topicPrefix v03.post should derive format v03."""
+    opts = make_options(post_topicPrefix=['v03', 'post'])
+    pub = Publisher(opts)
+    assert pub['format'] == 'v03'
+    assert pub['post_format'] == 'v03'
+
+
+def test_explicit_post_format_overrides_topicprefix():
+    """If user explicitly sets post_format, it wins over topicPrefix."""
+    opts = make_options(
+        post_format='v03',
+        post_topicPrefix=['v02', 'post'],
+    )
+    pub = Publisher(opts)
+    assert pub['format'] == 'v03'
+    assert pub['post_format'] == 'v03'
+
+
+def test_explicit_v02_post_format():
+    """If user explicitly sets post_format v02, use it."""
+    opts = make_options(post_format='v02')
+    pub = Publisher(opts)
+    assert pub['format'] == 'v02'
+    assert pub['post_format'] == 'v02'
+
+
+def test_topicprefix_fallback_is_empty_list():
+    """When neither post_topicPrefix nor topicPrefix is set, fallback must
+    be [] (empty list), not None. Peter fixed this in bab4b9424 -- None
+    causes TypeError when downstream code iterates or concatenates."""
+    opts = make_options()
+    del opts.post_topicPrefix
+    del opts.topicPrefix
+    pub = Publisher(opts)
+    assert pub['topicPrefix'] == [], \
+        "topicPrefix fallback must be [] not None (see commit bab4b9424)"
+
+
+def test_basedir_missing_no_keyerror():
+    """Publisher must not raise KeyError when baseDir is absent from the
+    dict. The guard must use 'or' (short-circuit) not 'and'."""
+    opts = make_options(post_baseUrl='file:/data/incoming')
+    del opts.post_baseDir
+    # This must not raise KeyError
+    pub = Publisher(opts)
+    assert pub['baseDir'] == '/data/incoming'
+
+
+def test_basedir_empty_string_derives_from_url():
+    """When baseDir is set but empty, it should still derive from baseUrl."""
+    opts = make_options(post_baseDir='', post_baseUrl='file:/data/output')
+    pub = Publisher(opts)
+    assert pub['baseDir'] == '/data/output'