diff --git a/pqm b/pqm
index b340441..74ea4f8 100755
--- a/pqm
+++ b/pqm
@@ -33,7 +33,7 @@ import yaml
 T = typing.TypeVar('T')
 
 
-@dataclasses.dataclass
+@dataclasses.dataclass(slots=True)
 class Config:
     # if not remote_sources are configured -> use local queue
     remote_sources: dict[str, str] = dataclasses.field(default_factory=dict)
@@ -157,7 +157,7 @@ async def trio_parallel_ordered(
         await tpo.close()
 
 
-@dataclasses.dataclass
+@dataclasses.dataclass(slots=True)
 class Recipient:
     """Recipient in a postfix mail"""
     address: str
@@ -199,7 +199,7 @@ def json_decode_stream(data: str):
         yield obj
 
 
-@dataclasses.dataclass
+@dataclasses.dataclass(slots=True)
 class Mail:
     """Metadata for mail in postfix queue"""
     queue_name: QueueName
@@ -233,6 +233,8 @@ class Mail:
 
 # abstract collection/cluster of postfix nodes (or just a single one)
 class Source(abc.ABC):
+    __slots__ = ()
+
     # list of server names in collection
     @abc.abstractmethod
     def server_list(self) -> list[str]:
@@ -331,6 +333,8 @@ class Source(abc.ABC):
 
 
 class LocalSource(Source):
+    __slots__ = ()
+
     def server_list(self) -> list[str]:
         return [socket.gethostname()]
 
@@ -388,6 +392,8 @@ class LocalSource(Source):
 
 
 class RemoteSource(Source):
+    __slots__ = ('remotes',)
+
     def __init__(self, remotes: dict[str, str]) -> None:
         super().__init__()
         self.remotes = remotes
@@ -520,6 +526,8 @@ class RemoteSource(Source):
 
 
 class UserActivityStats:
+    __slots__ = ('count_mails', 'related_mails', 'cut_off')
+
     # find most active address for `health` command
 
     def __init__(self, cut_off: int = 10) -> None:
@@ -588,6 +596,8 @@ class UserActivityStats:
 class Filter(abc.ABC):
     """abstract base class for filter expressions"""
 
+    __slots__ = ()
+
     def __init__(self) -> None:
         pass
 
@@ -650,11 +660,14 @@ class Filter(abc.ABC):
 
 # abstract base class for filters that don't need (...) around in representations of members in combined filters
 class SingleExprFilter(Filter):
-    pass
+    __slots__ = ()
 
 
 class FalseFilter(SingleExprFilter):
     """constant false - matches no mail"""
+
+    __slots__ = ()
+
     def __repr__(self) -> str:
         return '0'
 
@@ -680,6 +693,9 @@ class FalseFilter(SingleExprFilter):
 
 class TrueFilter(SingleExprFilter):
     """constant true - matches all mail"""
+
+    __slots__ = ()
+
     def __repr__(self) -> str:
         return '1'
 
@@ -708,6 +724,8 @@ TRUE_FILTER = TrueFilter()
 
 
 class AndFilter(Filter):
+    __slots__ = ('expressions',)
+
     def __init__(self, expressions: list[Filter] | tuple[()] = ()) -> None:
         super().__init__()
         self.expressions: list[Filter] = expressions or []
@@ -761,6 +779,8 @@ class AndFilter(Filter):
 
 
 class OrFilter(Filter):
+    __slots__ = ('expressions',)
+
     def __init__(self, expressions: list[Filter] | tuple[()] = ()) -> None:
         super().__init__()
         self.expressions: list[Filter] = expressions or []
@@ -814,6 +834,8 @@ class OrFilter(Filter):
 
 
 class NotFilter(SingleExprFilter):
+    __slots__ = ('expression',)
+
     def __init__(self, expression: Filter) -> None:
         super().__init__()
         self.expression = expression
@@ -851,6 +873,9 @@ class NotFilter(SingleExprFilter):
 
 class QueueFilter(SingleExprFilter):
     """match mails based on queue they are in"""
+
+    __slots__ = ('select',)
+
     def __init__(self, select: list[QueueName]) -> None:
         self.select = set(select)
 
@@ -909,6 +934,8 @@ class AddressSelector(enum.Enum):
 
 
 class BaseAddressPattern(abc.ABC):
+    __slots__ = ()
+
     # abstract base class of patterns to use to match a mail address
     # subclasses match either: full address, domain part, regex
     def __init__(self) -> None:
@@ -941,6 +968,8 @@ class BaseAddressPattern(abc.ABC):
 
 
 class AddressPattern(BaseAddressPattern):
+    __slots__ = ('address',)
+
     # match full address exactly
     def __init__(self, address: str) -> None:
         super().__init__()
@@ -963,6 +992,8 @@ class AddressPattern(BaseAddressPattern):
 
 
 class AddressDomainPattern(BaseAddressPattern):
+    __slots__ = ('domain',)
+
     # match address by domain
     def __init__(self, domain: str) -> None:
         super().__init__()
@@ -980,6 +1011,8 @@ class AddressDomainPattern(BaseAddressPattern):
 
 
 class AddressRegexMatch(BaseAddressPattern):
+    __slots__ = ('address',)
+
     # match address by regex
     def __init__(self, address: str | re.Pattern[str]) -> None:
         super().__init__()
@@ -1001,6 +1034,8 @@ class AddressRegexMatch(BaseAddressPattern):
 
 
 class AddressFilter(SingleExprFilter):
+    __slots__ = ('selector', 'patterns')
+
     # match mails by address
     def __init__(self, selector: AddressSelector, patterns: list[BaseAddressPattern]) -> None:
         self.selector = selector