diff --git a/requirements/main.in b/requirements/main.in
index 521bbf70fb93..6a388042e687 100644
--- a/requirements/main.in
+++ b/requirements/main.in
@@ -13,6 +13,7 @@ click
 cryptography>=43.0.1
 datadog>=0.19.0
 disposable-email-domains
+dnspython
 email-validator
 first
 forcediphttpsadapter
diff --git a/requirements/main.txt b/requirements/main.txt
index cfd7e5d0ec7f..627f3f8bb84f 100644
--- a/requirements/main.txt
+++ b/requirements/main.txt
@@ -520,7 +520,9 @@ disposable-email-domains==0.0.107 \
 dnspython==2.7.0 \
     --hash=sha256:b4c34b7d10b51bcc3a5071e7b8dee77939f1e878477eeecc965e9835f63c6c86 \
     --hash=sha256:ce9c432eda0dc91cf618a5cedf1a4e142651196bbcd2c80e89ed5a907e5cfaf1
-    # via email-validator
+    # via
+    #   -r requirements/main.in
+    #   email-validator
 docutils==0.21.2 \
     --hash=sha256:3a6b18732edf182daa3cd12775bbb338cf5691468f91eeeb109deff6ebfa986f \
     --hash=sha256:dafca5b9e384f0e419294eb4d2ff9fa826435bf15f15b7bd45723e8ad76811b2
diff --git a/warehouse/accounts/forms.py b/warehouse/accounts/forms.py
index efdcb6f452df..7e9e4489af2c 100644
--- a/warehouse/accounts/forms.py
+++ b/warehouse/accounts/forms.py
@@ -12,10 +12,12 @@
 
 from __future__ import annotations
 
+import contextlib
 import json
 import re
 
 import disposable_email_domains
+import dns.resolver
 import email_validator
 import humanize
 import markupsafe
@@ -301,6 +303,20 @@ def validate_email(self, field):
                 for _prio, mx_host in resp.mx
             }
 
+        # Resolve the returned MX domain's IP address to a PTR record, to a domain
+        all_mx_domains = set()
+        for mx_domain in mx_domains:
+            with contextlib.suppress(dns.resolver.NoAnswer, dns.resolver.NXDOMAIN):
+                mx_ip = dns.resolver.resolve(mx_domain, "A")
+                mx_ptr = dns.resolver.resolve_address(mx_ip[0].address)
+                mx_ptr_domain = extractor(
+                    mx_ptr[0].target.to_text().lower()
+                ).registered_domain
+                all_mx_domains.add(mx_ptr_domain)
+
+        # combine both sets
+        all_mx_domains.update(mx_domains)
+
         if (
             domain in disposable_email_domains.blocklist
             or self.request.db.query(
@@ -309,7 +325,7 @@ def validate_email(self, field):
                     & (ProhibitedEmailDomain.is_mx_record == False)  # noqa: E712
                 )
                 | exists().where(
-                    (ProhibitedEmailDomain.domain.in_(mx_domains))
+                    (ProhibitedEmailDomain.domain.in_(all_mx_domains))
                     & (ProhibitedEmailDomain.is_mx_record == True)  # noqa: E712
                 )
             ).scalar()
diff --git a/warehouse/locale/messages.pot b/warehouse/locale/messages.pot
index 76f6785fa667..55b7b4de5aaa 100644
--- a/warehouse/locale/messages.pot
+++ b/warehouse/locale/messages.pot
@@ -14,108 +14,108 @@ msgstr ""
 msgid "Locale updated"
 msgstr ""
 
-#: warehouse/accounts/forms.py:52 warehouse/accounts/forms.py:290
+#: warehouse/accounts/forms.py:54 warehouse/accounts/forms.py:292
 msgid "The email address isn't valid. Try again."
 msgstr ""
 
-#: warehouse/accounts/forms.py:53
+#: warehouse/accounts/forms.py:55
 msgid "The password is invalid. Try again."
 msgstr ""
 
-#: warehouse/accounts/forms.py:54
+#: warehouse/accounts/forms.py:56
 msgid ""
 "The username is invalid. Usernames must be composed of letters, numbers, "
 "dots, hyphens and underscores. And must also start and finish with a "
 "letter or number. Choose a different username."
 msgstr ""
 
-#: warehouse/accounts/forms.py:72
+#: warehouse/accounts/forms.py:74
 msgid "Null bytes are not allowed."
 msgstr ""
 
-#: warehouse/accounts/forms.py:86
+#: warehouse/accounts/forms.py:88
 msgid "No user found with that username"
 msgstr ""
 
-#: warehouse/accounts/forms.py:106
+#: warehouse/accounts/forms.py:108
 msgid "TOTP code must be ${totp_length} digits."
 msgstr ""
 
-#: warehouse/accounts/forms.py:126
+#: warehouse/accounts/forms.py:128
 msgid "Recovery Codes must be ${recovery_code_length} characters."
 msgstr ""
 
-#: warehouse/accounts/forms.py:141
+#: warehouse/accounts/forms.py:143
 msgid "Choose a username with 50 characters or less."
 msgstr ""
 
-#: warehouse/accounts/forms.py:158
+#: warehouse/accounts/forms.py:160
 msgid ""
 "This username is already being used by another account. Choose a "
 "different username."
 msgstr ""
 
-#: warehouse/accounts/forms.py:172 warehouse/accounts/forms.py:221
-#: warehouse/accounts/forms.py:234
+#: warehouse/accounts/forms.py:174 warehouse/accounts/forms.py:223
+#: warehouse/accounts/forms.py:236
 msgid "Password too long."
 msgstr ""
 
-#: warehouse/accounts/forms.py:208
+#: warehouse/accounts/forms.py:210
 msgid ""
 "There have been too many unsuccessful login attempts. You have been "
 "locked out for ${time}. Please try again later."
 msgstr ""
 
-#: warehouse/accounts/forms.py:237
+#: warehouse/accounts/forms.py:239
 msgid "Your passwords don't match. Try again."
 msgstr ""
 
-#: warehouse/accounts/forms.py:271
+#: warehouse/accounts/forms.py:273
 msgid "The email address is too long. Try again."
 msgstr ""
 
-#: warehouse/accounts/forms.py:322
+#: warehouse/accounts/forms.py:338
 msgid "You can't use an email address from this domain. Use a different email."
 msgstr ""
 
-#: warehouse/accounts/forms.py:337
+#: warehouse/accounts/forms.py:353
 msgid ""
 "This email address is already being used by this account. Use a different"
 " email."
 msgstr ""
 
-#: warehouse/accounts/forms.py:348
+#: warehouse/accounts/forms.py:364
 msgid ""
 "This email address is already being used by another account. Use a "
 "different email."
 msgstr ""
 
-#: warehouse/accounts/forms.py:388 warehouse/manage/forms.py:139
+#: warehouse/accounts/forms.py:404 warehouse/manage/forms.py:139
 #: warehouse/manage/forms.py:728
 msgid "The name is too long. Choose a name with 100 characters or less."
 msgstr ""
 
-#: warehouse/accounts/forms.py:395
+#: warehouse/accounts/forms.py:411
 msgid "URLs are not allowed in the name field."
 msgstr ""
 
-#: warehouse/accounts/forms.py:484
+#: warehouse/accounts/forms.py:500
 msgid "Invalid TOTP code."
 msgstr ""
 
-#: warehouse/accounts/forms.py:501
+#: warehouse/accounts/forms.py:517
 msgid "Invalid WebAuthn assertion: Bad payload"
 msgstr ""
 
-#: warehouse/accounts/forms.py:570
+#: warehouse/accounts/forms.py:586
 msgid "Invalid recovery code."
 msgstr ""
 
-#: warehouse/accounts/forms.py:579
+#: warehouse/accounts/forms.py:595
 msgid "Recovery code has been previously used."
 msgstr ""
 
-#: warehouse/accounts/forms.py:609
+#: warehouse/accounts/forms.py:625
 msgid "The username isn't valid. Try again."
 msgstr ""