diff --git a/apps/admin-x-settings/src/components/settings/email/newsletters/NewsletterDetailModal.tsx b/apps/admin-x-settings/src/components/settings/email/newsletters/NewsletterDetailModal.tsx
index a90fdfd4b3..aefd3c2845 100644
--- a/apps/admin-x-settings/src/components/settings/email/newsletters/NewsletterDetailModal.tsx
+++ b/apps/admin-x-settings/src/components/settings/email/newsletters/NewsletterDetailModal.tsx
@@ -197,28 +197,15 @@ const Sidebar: React.FC<{
 
         // Pro users with custom sending domains
         if (hasSendingDomain(config)) {
-            let sendingEmail = newsletter.sender_email || ''; // Do not use the rendered address here, because this field is editable and we otherwise can't have an empty field
-
-            // It is possible we have an invalid saved email address, in that case it won't get used
-            // so we should display as if we are using the default = an empty address
-            if (sendingEmail && sendingEmail !== newsletterAddress) {
-                sendingEmail = '';
-            }
-
-            const sendingEmailUsername = sendingEmail?.split('@')[0] || '';
-
             return (
                 <TextField
                     error={Boolean(errors.sender_email)}
                     hint={errors.sender_email}
                     placeholder={defaultEmailAddress}
-                    rightPlaceholder={sendingEmailUsername ? `@${sendingDomain(config)}` : `` }
                     title="Sender email address"
-                    value={sendingEmailUsername || ''}
+                    value={newsletter.sender_email || ''}
                     onChange={(e) => {
-                        const username = e.target.value?.split('@')[0];
-                        const newEmail = username ? `${username}@${sendingDomain(config)}` : '';
-                        updateNewsletter({sender_email: newEmail});
+                        updateNewsletter({sender_email: e.target.value});
                     }}
                     onKeyDown={() => clearError('sender_email')}
                 />
@@ -573,6 +560,8 @@ const NewsletterDetailModalContent: React.FC<{newsletter: Newsletter; onlyOne: b
 
             if (formState.sender_email && !validator.isEmail(formState.sender_email)) {
                 newErrors.sender_email = 'Invalid email';
+            } else if (formState.sender_email && hasSendingDomain(config) && formState.sender_email.split('@')[1] !== sendingDomain(config)) {
+                newErrors.sender_email = `Email must end with @${sendingDomain(config)}`;
             }
 
             if (formState.sender_reply_to && !validator.isEmail(formState.sender_reply_to) && !['newsletter', 'support'].includes(formState.sender_reply_to)) {
diff --git a/apps/admin-x-settings/src/utils/newsletterEmails.ts b/apps/admin-x-settings/src/utils/newsletterEmails.ts
index bb903ad5aa..febad178ed 100644
--- a/apps/admin-x-settings/src/utils/newsletterEmails.ts
+++ b/apps/admin-x-settings/src/utils/newsletterEmails.ts
@@ -1,4 +1,4 @@
-import {Config, hasSendingDomain, isManagedEmail, sendingDomain} from '@tryghost/admin-x-framework/api/config';
+import {Config, hasSendingDomain, isManagedEmail} from '@tryghost/admin-x-framework/api/config';
 import {Newsletter} from '@tryghost/admin-x-framework/api/newsletters';
 
 export const renderSenderEmail = (newsletter: Newsletter, config: Config, defaultEmailAddress: string|undefined) => {
@@ -7,15 +7,6 @@ export const renderSenderEmail = (newsletter: Newsletter, config: Config, defaul
         return defaultEmailAddress;
     }
 
-    if (isManagedEmail(config) && hasSendingDomain(config)) {
-        // Only return sender_email if the domain names match
-        if (newsletter.sender_email?.split('@')[1] === sendingDomain(config)) {
-            return newsletter.sender_email;
-        } else {
-            return defaultEmailAddress || '';
-        }
-    }
-
     return newsletter.sender_email || defaultEmailAddress || '';
 };
 
diff --git a/apps/admin-x-settings/test/acceptance/email/newsletters.test.ts b/apps/admin-x-settings/test/acceptance/email/newsletters.test.ts
index ead7f535d0..08f5e58539 100644
--- a/apps/admin-x-settings/test/acceptance/email/newsletters.test.ts
+++ b/apps/admin-x-settings/test/acceptance/email/newsletters.test.ts
@@ -252,7 +252,7 @@ test.describe('Newsletter settings', async () => {
         });
 
         test.describe('For Ghost (Pro) users with custom sending domain', () => {
-            test('Allow sender address to be changed partially (username but not domain name)', async ({page}) => {
+            test('The sender email address can be changed partially (username but not domain name)', async ({page}) => {
                 await mockApi({page, requests: {
                     ...globalDataRequests,
                     browseNewsletters: {method: 'GET', path: '/newsletters/?include=count.active_members%2Ccount.posts&limit=50', response: responseFixtures.newsletters},
@@ -284,11 +284,20 @@ test.describe('Newsletter settings', async () => {
                 const modal = page.getByTestId('newsletter-modal');
                 const senderEmail = modal.getByLabel('Sender email');
 
-                // The sender email field should keep the username part of the email address
-                await senderEmail.fill('harry@potter.com');
-                expect(await senderEmail.inputValue()).toBe('harry');
+                // Error case #1: add invalid email address
+                await senderEmail.fill('Harry Potter');
+                await modal.getByRole('button', {name: 'Save'}).click();
+                await expect(page.getByTestId('toast-error').first()).toHaveText(/Can't save newsletter/);
+                await expect(modal).toHaveText(/Invalid email/);
 
-                // The new username is saved without a confirmation popup
+                // Error case #2: the sender email address doesn't match the custom sending domain
+                await senderEmail.fill('harry@potter.com');
+                await modal.getByRole('button', {name: 'Save'}).click();
+                await expect(page.getByTestId('toast-error').first()).toHaveText(/Can't save newsletter/);
+                await expect(modal).toHaveText(/Email must end with @customdomain.com/);
+
+                // But can have any address on the same domain, without verification
+                await senderEmail.fill('harry@customdomain.com');
                 await modal.getByRole('button', {name: 'Save'}).click();
                 await expect(page.getByTestId('confirmation-modal')).toHaveCount(0);
             });