diff --git a/verify.py b/verify.py
index de16b75..116f43d 100644
--- a/verify.py
+++ b/verify.py
@@ -5,33 +5,105 @@
 
 import io
 import sys
+from collections import Counter
 
 from publicsuffixlist import PublicSuffixList
 from requests import get
 
-def main(arguments):
+
+blacklist = "disposable_email_blacklist.conf"
+whitelist = "whitelist.conf"
+
+files = {
+    filename: open(filename).read().splitlines() for filename in [whitelist, blacklist]
+}
+
+
+def download_suffixes():
+    with open("public_suffix_list.dat", "wb") as file:
+        response = get("https://publicsuffix.org/list/public_suffix_list.dat")
+        file.write(response.content)
+
+
+def check_for_public_suffixes(filename):
+    lines = files[filename]
     suffix_detected = False
     psl = None
     download_suffixes()
     with open("public_suffix_list.dat", "r") as latest:
         psl = PublicSuffixList(latest)
-    with io.open('disposable_email_blacklist.conf', 'r') as deb:
-        for i, line in enumerate(deb):
-            current_line = line.strip()
-            public_suffix = psl.publicsuffix(current_line)
-            if public_suffix == current_line:
-                print(f'The line number {i+1} contains just a public suffix: {current_line}')
-                suffix_detected = True
+    for i, line in enumerate(lines):
+        current_line = line.strip()
+        public_suffix = psl.publicsuffix(current_line)
+        if public_suffix == current_line:
+            print(
+                f"The line number {i+1} contains just a public suffix: {current_line}"
+            )
+            suffix_detected = True
     if suffix_detected:
-        print ('At least one valid public suffix found in the blacklist, please remove it. See https://publicsuffix.org for details on why this shouldn\'t be blacklisted.')
+        print(
+            "At least one valid public suffix found in {!r}, please "
+            "remove it. See https://publicsuffix.org for details on why this "
+            "shouldn't be blacklisted.".format(filename)
+        )
         sys.exit(1)
 
-def download_suffixes():
-    with open('public_suffix_list.dat', "wb") as file:
-        response = get('https://publicsuffix.org/list/public_suffix_list.dat')
-        file.write(response.content)
 
+def check_for_non_lowercase(filename):
+    lines = files[filename]
+    invalid = set(lines) - set(line.lower() for line in lines)
+    if invalid:
+        print("The following domains should be lowercased in {!r}:".format(filename))
+        for line in sorted(invalid):
+            print("* {}".format(line))
+        sys.exit(1)
+
+
+def check_for_duplicates(filename):
+    lines = files[filename]
+    count = Counter(lines) - Counter(set(lines))
+    if count:
+        print("The following domains appear twice in {!r}:".format(filename))
+        for line in sorted(count):
+            print("* {}".format(line))
+        sys.exit(1)
+
+
+def check_sort_order(filename):
+    lines = files[filename]
+    for a, b in zip(lines, sorted(lines)):
+        if a != b:
+            print("The list is not sorted in {!r}:".format(filename))
+            print("* {!r} should come before {!r}".format(b, a))
+            sys.exit(1)
+
+
+def check_for_intersection(filename_a, filename_b):
+    a = files[filename_a]
+    b = files[filename_b]
+    intersection = set(a) & set(b)
+    if intersection:
+        print("The following domains appear in both lists:")
+        for line in sorted(intersection):
+            print("* {}".format(line))
 
 
 if __name__ == "__main__":
-    main(sys.argv)
+
+    # Check if any domains have a public suffix
+    check_for_public_suffixes(blacklist)
+
+    # Check if any domains are not lowercase
+    check_for_non_lowercase(whitelist)
+    check_for_non_lowercase(blacklist)
+
+    # Check if any domains are duplicated in the same list
+    check_for_duplicates(whitelist)
+    check_for_duplicates(blacklist)
+
+    # Check if any lists are not sorted
+    check_sort_order(whitelist)
+    check_sort_order(blacklist)
+
+    # Check if any domains are in both the whitelist and blacklist
+    check_for_intersection(whitelist, blacklist)