diff --git a/src/registrar/forms/portfolio.py b/src/registrar/forms/portfolio.py
index b83e718cb..2ee174050 100644
--- a/src/registrar/forms/portfolio.py
+++ b/src/registrar/forms/portfolio.py
@@ -22,6 +22,7 @@ from registrar.models.utility.portfolio_helper import (
     get_domains_display,
     get_members_description_display,
     get_members_display,
+    get_portfolio_invitation_associations,
 )
 
 logger = logging.getLogger(__name__)
@@ -459,7 +460,14 @@ class PortfolioNewMemberForm(BasePortfolioMemberForm):
             if hasattr(e, "code"):
                 field = "email" if "email" in self.fields else None
                 if e.code == "has_existing_permissions":
-                    self.add_error(field, f"{self.instance.email} is already a member of another .gov organization.")
+                    existing_permissions, existing_invitations = (
+                        get_portfolio_invitation_associations(self.instance)
+                    )
+
+                    same_portfolio_for_permissions = existing_permissions.exclude(portfolio=self.instance.portfolio)
+                    same_portfolio_for_invitations = existing_invitations.exclude(portfolio=self.instance.portfolio)
+                    if same_portfolio_for_permissions.exists() or same_portfolio_for_invitations.exists():
+                        self.add_error(field, f"{self.instance.email} is already a member of another .gov organization.")
                     override_error = True
                 elif e.code == "has_existing_invitations":
                     self.add_error(
diff --git a/src/registrar/models/utility/portfolio_helper.py b/src/registrar/models/utility/portfolio_helper.py
index 009ea3c26..707dfcf54 100644
--- a/src/registrar/models/utility/portfolio_helper.py
+++ b/src/registrar/models/utility/portfolio_helper.py
@@ -286,8 +286,8 @@ def validate_user_portfolio_permission(user_portfolio_permission):
 
     # == Validate the multiple_porfolios flag. == #
     if not flag_is_active_for_user(user_portfolio_permission.user, "multiple_portfolios"):
-        existing_permissions = UserPortfolioPermission.objects.exclude(id=user_portfolio_permission.id).filter(
-            user=user_portfolio_permission.user
+        existing_permissions, existing_invitations = (
+            get_user_portfolio_permission_associations(user_portfolio_permission)
         )
         if existing_permissions.exists():
             raise ValidationError(
@@ -296,10 +296,6 @@ def validate_user_portfolio_permission(user_portfolio_permission):
                 code="has_existing_permissions",
             )
 
-        existing_invitations = PortfolioInvitation.objects.filter(email=user_portfolio_permission.user.email).exclude(
-            Q(portfolio=user_portfolio_permission.portfolio)
-            | Q(status=PortfolioInvitation.PortfolioInvitationStatus.RETRIEVED)
-        )
         if existing_invitations.exists():
             raise ValidationError(
                 "This user is already assigned to a portfolio invitation. "
@@ -307,6 +303,29 @@ def validate_user_portfolio_permission(user_portfolio_permission):
                 code="has_existing_invitations",
             )
 
+def get_user_portfolio_permission_associations(user_portfolio_permission):
+    """
+    Retrieves the associations for a user portfolio invitation.
+
+    Returns:
+      A tuple:
+        (existing_permissions, existing_invitations)
+      where:
+        - existing_permissions: UserPortfolioPermission objects excluding the current permission.
+        - existing_invitations: PortfolioInvitation objects for the user email excluding 
+        the current invitation and those with status RETRIEVED.
+    """
+    PortfolioInvitation = apps.get_model("registrar.PortfolioInvitation")
+    UserPortfolioPermission = apps.get_model("registrar.UserPortfolioPermission")
+    existing_permissions = UserPortfolioPermission.objects.exclude(id=user_portfolio_permission.id).filter(
+        user=user_portfolio_permission.user
+    )
+    existing_invitations = PortfolioInvitation.objects.filter(email__iexact=user_portfolio_permission.user.email).exclude(
+        Q(portfolio=user_portfolio_permission.portfolio)
+        | Q(status=PortfolioInvitation.PortfolioInvitationStatus.RETRIEVED)
+    )
+    return (existing_permissions, existing_invitations)
+
 
 def validate_portfolio_invitation(portfolio_invitation):
     """
@@ -351,17 +370,14 @@ def validate_portfolio_invitation(portfolio_invitation):
         )
 
     # == Validate the multiple_porfolios flag. == #
-    user = User.objects.filter(email=portfolio_invitation.email).first()
+    user = User.objects.filter(email__iexact=portfolio_invitation.email).first()
 
     # If user returns None, then we check for global assignment of multiple_portfolios.
     # Otherwise we just check on the user.
     if not flag_is_active_for_user(user, "multiple_portfolios"):
-        existing_permissions = UserPortfolioPermission.objects.filter(user=user)
-
-        existing_invitations = PortfolioInvitation.objects.filter(email=portfolio_invitation.email).exclude(
-            Q(id=portfolio_invitation.id) | Q(status=PortfolioInvitation.PortfolioInvitationStatus.RETRIEVED)
+        existing_permissions, existing_invitations = (
+            get_portfolio_invitation_associations(portfolio_invitation)
         )
-
         if existing_permissions.exists():
             raise ValidationError(
                 "This user is already assigned to a portfolio. "
@@ -376,6 +392,26 @@ def validate_portfolio_invitation(portfolio_invitation):
                 code="has_existing_invitations",
             )
 
+def get_portfolio_invitation_associations(portfolio_invitation):
+    """
+    Retrieves the associations for a portfolio invitation.
+
+    Returns:
+      A tuple:
+        (existing_permissions, existing_invitations)
+      where:
+        - existing_permissions: UserPortfolioPermission objects matching the email.
+        - existing_invitations: PortfolioInvitation objects for the email excluding 
+        the current invitation and those with status RETRIEVED.
+    """
+    PortfolioInvitation = apps.get_model("registrar.PortfolioInvitation")
+    UserPortfolioPermission = apps.get_model("registrar.UserPortfolioPermission")
+    existing_permissions = UserPortfolioPermission.objects.filter(user__email__iexact=portfolio_invitation.email)
+    existing_invitations = PortfolioInvitation.objects.filter(email__iexact=portfolio_invitation.email).exclude(
+        Q(id=portfolio_invitation.id) | Q(status=PortfolioInvitation.PortfolioInvitationStatus.RETRIEVED)
+    )
+    return (existing_permissions, existing_invitations)
+
 
 def cleanup_after_portfolio_member_deletion(portfolio, email, user=None):
     """