Gmail Send Mail As Error: 535 Incorrect Authentication Data

If Gmail bounces your message with "535 Incorrect authentication data" and a CustomFromDenied help link, saying your "Send mail as" settings are misconfigured or out of date, the fix is almost always the same. Gmail is trying to relay through your Ultra Web Hosting mailbox with a password that no longer matches. This guide shows you how to update the stored SMTP password so your outgoing mail works again.

01. What This Bounce Actually Means

The full bounce looks like this:

Message not delivered
You're sending this from a different address or alias using the
'Send mail as' feature. The settings for your 'Send mail as' account
are misconfigured or out of date. Check those settings and try resending.
LEARN MORE https://support.google.com/mail/?p=CustomFromDenied
The response from the remote server was:
535 Incorrect authentication data

Two things are worth separating here, because they come from two different places:

• "535 Incorrect authentication data" is the response from our mail server. It means a program tried to log in to your mailbox to send a message and the username or password was wrong. The 535 code is specifically an authentication failure, not a connection or spam problem.
• The "Send mail as" and CustomFromDenied wording is Gmail's interpretation of that 535. Gmail is telling you that the outbound settings it has stored for your custom address are what got rejected.

So the message is accurate: the credentials Gmail is using to send on your behalf no longer work. Nothing is wrong with the message you tried to send, and it is not lost. Gmail simply could not hand it to our server.

02. Why the Password Stopped Working

Gmail does not ask our server for your password each time. When you first set up "Send mail as", you typed your mailbox password into Gmail once, and Gmail saved it. From then on it uses that saved copy. The 535 appears when the saved copy and the real mailbox password drift apart. The usual reasons, in order of how often we see them:

1. The mailbox password was changed in cPanel and the new one was never entered in Gmail. This is by far the most common cause. Changing the password anywhere (cPanel, webmail, a password reset) invalidates the copy Gmail is holding.
2. The wrong password was saved to begin with - for example the cPanel login password instead of the individual email account password. These are two different passwords. "Send mail as" needs the email account password.
3. The username is not the full email address. Our server expects the complete address ([email protected]) as the login name, not just the part before the @.
4. The mailbox was deleted or renamed. If the email account no longer exists exactly as spelled in Gmail, every login fails.

03. The Fix: Re-Enter Your Password in Gmail

If you are not certain what the current mailbox password is, reset it first so you know it for sure:

1. Log in to cPanel and open Email Accounts.
2. Find the address that appears in the bounce, click Manage, and set a New Password. Choose something long and copy it somewhere you can paste from.
3. Save the change.

Now update the copy Gmail is holding:

1. In Gmail on a computer, click the gear icon and choose See all settings.
2. Open the Accounts and Import tab.
3. In the Send mail as section, find your domain address and click edit info next to it.
4. In the window that opens, click Next Step until you reach the SMTP server screen. Confirm the SMTP Server, Port, and Username match the settings in the next section, then type the current mailbox password into the Password field.
5. Click Save Changes.

Send yourself a test message from the domain address. If it goes through, you are done. The message that originally bounced was not queued, so resend it.

04. Correct SMTP Settings to Use

While you are in the "Send mail as" editor, make sure every field matches these values. A wrong port or hostname will also produce a failure, though usually a connection error rather than a 535.

SMTP Server:  yourserver.ultrawebhosting.com
Port:         465
Connection:   Secured connection using SSL
Username:     full email address ([email protected])
Password:     your email account password (set in cPanel)

If your setup was built around TLS instead of SSL, this combination is also valid:

SMTP Server:  yourserver.ultrawebhosting.com
Port:         587
Connection:   Secured connection using TLS
Username:     full email address ([email protected])
Password:     your email account password (set in cPanel)

05. If It Still Says 535

If Gmail still rejects the password after you have re-entered it, work through these in order:

• Retype the password by hand. Pasting can pull in a trailing space or a hidden character. Type it directly, slowly, and watch for autocorrect on the first letter.
• Confirm you are using the email account password, not the cPanel password. Reset the email account password in cPanel again and paste that exact value into both places if you are unsure which is which.
• Check the username is the full address. It must read [email protected], not you.
• Confirm the mailbox still exists under cPanel > Email Accounts, spelled exactly as it is in Gmail. A renamed or removed account cannot authenticate.
• Log in to webmail with the same address and password at https://yourdomain.com/webmail. If webmail rejects them too, the credentials themselves are the problem and the fix is entirely in cPanel. If webmail accepts them, re-check what Gmail has stored.
• Try the other port and security pairing - 465 with SSL, or 587 with TLS - in case a firewall or the network you are on interferes with one of them.

06. Alternatives Worth Knowing About

Fixing the password is the direct answer, but two alternatives are worth knowing about depending on how you prefer to work.

Use webmail or a mail client instead of Gmail

If you would rather not route your domain mail through a personal Gmail account at all, you can read and send it directly. Webmail works from any browser with no setup, and a desktop or phone client connects with the same settings above. See our setup guides for Microsoft Outlook, iPhone or iPad, and Android, plus POP3 vs IMAP if you are deciding how to connect.

Run your domain mail on Google Workspace

If the reason you use "Send mail as" is that you genuinely prefer Gmail's interface for your business address, Google Workspace lets your domain live inside Google natively, with no relay password to maintain. It is a paid Google product, separate from your hosting, but it removes this class of problem entirely. See How to Set Up Google Workspace Email With Your Domain.

Quick Recap: Clearing the 535 Bounce

If you only do these things, do these:

1. Recognize the cause - 535 is an authentication failure, so Gmail's stored "Send mail as" password no longer matches your mailbox
2. Reset the email account password in cPanel under Email Accounts, so you know the current value for certain
3. Re-enter that password in Gmail under Settings > Accounts and Import > Send mail as > edit info
4. Verify the fields - full email address as the username, port 465 SSL (or 587 TLS), your server hostname
5. Send a test message and resend anything that bounced, since it was not queued

Last updated September 2026 · Browse all Email and Webmail articles