{"id":3564,"date":"2023-11-23T10:25:51","date_gmt":"2023-11-23T10:25:51","guid":{"rendered":"https:\/\/www.warmy.io\/blog\/google-error-535-5-7-8-username-and-password-not-accepted\/"},"modified":"2026-07-08T10:03:18","modified_gmt":"2026-07-08T10:03:18","slug":"google-error-535-5-7-8-username-and-password-not-accepted","status":"publish","type":"post","link":"https:\/\/www.warmy.io\/blog\/google-error-535-5-7-8-username-and-password-not-accepted\/","title":{"rendered":"SMTP Error 535 5.7.8: Username and Password Not Accepted \u2014 Causes and Fixes"},"content":{"rendered":"\n

SMTP error 535 5.7.8 means your email server rejected your login credentials during authentication. The most common triggers are a wrong password, missing App Password when 2FA is active, or Google’s removal of basic authentication \u2014 which now requires OAuth 2.0 or an App Password. Fix it by verifying credentials, generating an App Password, or switching your email client to OAuth. This guide covers all causes and fixes for Gmail, Outlook, and beyond.<\/p>\n\n\n\n

When you see the 535-5.7.8 Username and Password not accepted message, your SMTP server is telling you one thing clearly: it cannot verify your identity. The fix depends on which of the seven causes below applies to your setup \u2014 and one of them is now almost universal for Gmail users. In May 2025, Google permanently ended basic password authentication for all accounts (personal and Workspace). If you haven’t switched to OAuth 2.0 or App Passwords yet, that alone is likely the cause of your error.<\/p>\n\n\n\n

Defined in IETF RFC 4954<\/a>, the 535 5.7.8 code applies across all email providers \u2014 Gmail, Outlook, Yahoo, and any private SMTP server. Email clients like Outlook, Thunderbird, and Apple Mail all return it when the auth handshake fails. This guide covers every cause and every fix, from the simplest credential check to App Password generation and OAuth migration.<\/p>\n\n\n\n

Quick Cause-and-Fix Reference<\/h2>\n\n\n\n
Cause<\/strong><\/th>Fastest Fix<\/strong><\/th><\/tr><\/thead>
Wrong username\/password<\/td>Double-check credentials; reset if needed<\/td><\/tr>
2FA enabled \u2014 no App Password<\/td>Generate a 16-char App Password in Google Account > Security<\/td><\/tr>
Basic auth (Gmail\/Workspace)<\/td>Switch to OAuth 2.0 or use an App Password<\/td><\/tr>
Wrong SMTP settings<\/td>smtp.gmail.com \u2502 Port 587 (TLS) or 465 (SSL)<\/td><\/tr>
IP blacklisted<\/td>Check with Warmy’s free deliverability test; contact ISP<\/td><\/tr>
Firewall\/antivirus blocking port<\/td>Whitelist ports 465, 587 in firewall rules<\/td><\/tr>
Wrong encryption method<\/td>Switch to TLS (STARTTLS) or SSL\/TLS as required<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Common Causes of “535-5.7.8 Username and Password Not Accepted”<\/h2>\n\n\n\n

1. Invalid Username or Password<\/h3>\n\n\n\n

A typo or outdated password is still the most frequent cause. Remember that Gmail usernames and passwords are case-sensitive, and you must use your full email address as the username \u2014 not just the handle before the @ symbol.<\/p>\n\n\n\n

2. Two-Factor Authentication Without an App Password<\/h3>\n\n\n\n

When 2FA (two-step verification) is enabled on your Google account, your regular account password no longer works for third-party email clients. Google requires you to generate a dedicated App Password \u2014 a 16-character code that authenticates the specific app or device without exposing your main password.<\/p>\n\n\n\n

3. Google’s Removal of Basic Authentication (Critical 2025 Update)<\/h3>\n\n\n\n

This is now the primary cause of SMTP Error 535 5.7.8 for Gmail and Google Workspace users. Google permanently ended “Less Secure Apps” access \u2014 personal Gmail accounts lost it in May 2022, and all Google Workspace accounts lost it in May 2025. Google’s own documentation<\/a> confirms: “Starting March 14, 2025, you and your users must use OAuth with third-party apps to access Gmail.” Any email client still using a plain username and password will receive the SMTP error 535 5.7.8 \u2014 regardless of whether the credentials are correct.<\/p>\n\n\n\n

4. Incorrect SMTP Server Settings<\/h3>\n\n\n\n

Using the wrong SMTP server address, port, or encryption method causes the connection to fail before authentication even begins. Google requires smtp.gmail.com on Port 587 (TLS\/STARTTLS) or Port 465 (SSL). If your client is connecting on Port 25 or without encryption, it will be rejected.<\/p>\n\n\n\n

5. IP Blacklisting<\/h3>\n\n\n\n

If your sending IP address has been flagged for suspicious activity or spam, Google’s SMTP server may reject your login \u2014 even with correct credentials. This is less obvious because the error message looks identical to a password failure.<\/p>\n\n\n\n

6. Firewall or Antivirus Blocking SMTP Traffic<\/h3>\n\n\n\n

Security software sometimes flags outbound SMTP traffic on ports 465 or 587 as suspicious. This interrupts the authentication handshake and results in a 535 error.<\/p>\n\n\n\n

7. Encryption Mismatch<\/h3>\n\n\n\n

If your email client is configured to use SSL when the server requires TLS (STARTTLS), or vice versa, the connection will fail at the encryption negotiation stage \u2014 before credentials are even checked.<\/p>\n\n\n\n

How to Fix Error 535-5.7.8: Step-by-Step<\/h2>\n\n\n\n

1. Verify Your Username and Password<\/h3>\n\n\n\n

Start by confirming you’re using the correct credentials. For Gmail, the username is always your full email address (including @gmail.com or your Workspace domain). If you are uncertain whether your password is correct, reset it directly from your Google Account before attempting any other fix. A typo or outdated password is still the most frequent cause. Before troubleshooting further, use a password checker<\/a> to verify your saved credentials if needed. Remember that Gmail usernames and passwords are case-sensitive, and you must use your full email address as the username \u2014 not just the handle before the @ symbol.<\/p>\n\n\n\n

2. Generate an App Password (If 2FA Is Active)<\/h3>\n\n\n\n

If two-step verification is enabled, you need an App Password for your email client:<\/p>\n\n\n\n