diff --git a/stdlib/smtplib.pyi b/stdlib/smtplib.pyi
index 2d03b60e7bb4..5f9ebab033b5 100644
--- a/stdlib/smtplib.pyi
+++ b/stdlib/smtplib.pyi
@@ -1,5 +1,5 @@
 import sys
-from _typeshed import Self
+from _typeshed import ReadableBuffer, Self, _BufferWithLen
 from collections.abc import Sequence
 from email.message import Message as _Message
 from re import Pattern
@@ -9,6 +9,8 @@ from types import TracebackType
 from typing import Any, Protocol, overload
 from typing_extensions import TypeAlias
 
+from _socket import _Address as _SourceAddress
+
 __all__ = [
     "SMTPException",
     "SMTPServerDisconnected",
@@ -28,8 +30,6 @@ __all__ = [
 
 _Reply: TypeAlias = tuple[int, bytes]
 _SendErrs: TypeAlias = dict[str, _Reply]
-# Should match source_address for socket.create_connection
-_SourceAddress: TypeAlias = tuple[bytearray | bytes | str, int]
 
 SMTP_PORT: int
 SMTP_SSL_PORT: int
@@ -102,7 +102,7 @@ class SMTP:
     ) -> None: ...
     def set_debuglevel(self, debuglevel: int) -> None: ...
     def connect(self, host: str = ..., port: int = ..., source_address: _SourceAddress | None = ...) -> _Reply: ...
-    def send(self, s: bytes | str) -> None: ...
+    def send(self, s: ReadableBuffer | str) -> None: ...
     def putcmd(self, cmd: str, args: str = ...) -> None: ...
     def getreply(self) -> _Reply: ...
     def docmd(self, cmd: str, args: str = ...) -> _Reply: ...
@@ -114,7 +114,7 @@ class SMTP:
     def noop(self) -> _Reply: ...
     def mail(self, sender: str, options: Sequence[str] = ...) -> _Reply: ...
     def rcpt(self, recip: str, options: Sequence[str] = ...) -> _Reply: ...
-    def data(self, msg: bytes | str) -> _Reply: ...
+    def data(self, msg: ReadableBuffer | str) -> _Reply: ...
     def verify(self, address: str) -> _Reply: ...
     vrfy = verify
     def expn(self, address: str) -> _Reply: ...
@@ -125,16 +125,16 @@ class SMTP:
     @overload
     def auth_cram_md5(self, challenge: None = ...) -> None: ...
     @overload
-    def auth_cram_md5(self, challenge: bytes) -> str: ...
-    def auth_plain(self, challenge: bytes | None = ...) -> str: ...
-    def auth_login(self, challenge: bytes | None = ...) -> str: ...
+    def auth_cram_md5(self, challenge: ReadableBuffer) -> str: ...
+    def auth_plain(self, challenge: ReadableBuffer | None = ...) -> str: ...
+    def auth_login(self, challenge: ReadableBuffer | None = ...) -> str: ...
     def login(self, user: str, password: str, *, initial_response_ok: bool = ...) -> _Reply: ...
     def starttls(self, keyfile: str | None = ..., certfile: str | None = ..., context: SSLContext | None = ...) -> _Reply: ...
     def sendmail(
         self,
         from_addr: str,
         to_addrs: str | Sequence[str],
-        msg: bytes | str,
+        msg: _BufferWithLen | str,
         mail_options: Sequence[str] = ...,
         rcpt_options: Sequence[str] = ...,
     ) -> _SendErrs: ...