diff --git a/sslyze/connection_helpers/opportunistic_tls_helpers.py b/sslyze/connection_helpers/opportunistic_tls_helpers.py
index 1a45069f..b962668e 100644
--- a/sslyze/connection_helpers/opportunistic_tls_helpers.py
+++ b/sslyze/connection_helpers/opportunistic_tls_helpers.py
@@ -2,6 +2,7 @@
 import struct
 from abc import abstractmethod, ABC
 from enum import Enum
+from smtplib import SMTP, SMTPException
 from typing import ClassVar, Optional
 
 
@@ -65,19 +66,37 @@ def __init__(self, smtp_ehlo_hostname: str):
         self._smtp_ehlo_hostname = smtp_ehlo_hostname
 
     def prepare_socket_for_tls_handshake(self, sock: socket.socket) -> None:
-        # Get the SMTP banner
-        sock.recv(2048)
+        # SMTP parsing has some complicated areas and some unusual but legal
+        # server behavior - this code uses Python's smtplib to handle the protocol.
+        smtp = SMTP(local_hostname=self._smtp_ehlo_hostname)
+        smtp.sock = sock
 
-        # Send a EHLO and wait for the 250 status
-        sock.send(f"EHLO {self._smtp_ehlo_hostname}\r\n".encode("ascii"))
-        data = sock.recv(2048)
-        if b"250 " not in data:
-            raise OpportunisticTlsError(f"SMTP EHLO was rejected: {repr(data)}")
+        try:
+            code, server_reply = smtp.getreply()
+            message = server_reply.decode()
+        except SMTPException as exc:
+            code, message = -1, str(exc)
+        if code != 220:
+            raise OpportunisticTlsError(f"Unable to find 220 service ready response: {message}")
+
+        try:
+            code, server_reply = smtp.getreply()
+            message = server_reply.decode()
+        except SMTPException as exc:
+            code, message = -1, str(exc)
+        if code != 250:
+            raise OpportunisticTlsError(f"SMTP EHLO was rejected: {message}")
+
+        if not smtp.has_extn("starttls"):
+            raise OpportunisticTlsError(f"Server does not support STARTTLS: {message}")
 
-        # Send a STARTTLS
-        sock.send(b"STARTTLS\r\n")
-        if b"220" not in sock.recv(2048):
-            raise OpportunisticTlsError("SMTP STARTTLS not supported")
+        try:
+            code, server_reply = smtp.getreply()
+            message = server_reply.decode()
+        except SMTPException as exc:
+            code, message = -1, str(exc)
+        if code != 220:
+            raise OpportunisticTlsError(f"SMTP STARTTLS rejected: {message}")
 
 
 class _XmppHelper(_OpportunisticTlsHelper):