SMTP Error 535 5.7.8: Username and Password Not Accepted (Fix Guide) Print

SMTP error 535 5.7.8 ("Username and Password not accepted") means your mail server rejected your login credentials during authentication. It shows up across virtually every major provider and email client, and while the message looks alarming, the fix is usually one of a handful of well-understood causes.

Quick cause-and-fix reference

• Wrong username or password: Double-check credentials, and reset the password if you're unsure.
• Two-factor authentication enabled, no app password: Generate an app-specific password from your account's security settings.
• Basic authentication no longer supported: Switch to OAuth2 or an app password — many providers have fully retired plain password logins for third-party clients.
• Wrong SMTP server settings: Confirm the correct server address and port (commonly 587 for TLS or 465 for SSL) for your provider.
• Sending IP flagged or blacklisted: Some providers reject authentication attempts from IPs with a poor reputation, even with correct credentials.
• Firewall or antivirus blocking the port: Whitelist ports 465 and 587 in your firewall rules.
• Encryption mismatch: Make sure your client's encryption setting (TLS/STARTTLS vs. SSL) matches what the server expects.

Step-by-step fix

1. Verify your username and password: Use your full email address as the username, and confirm capitalization is correct. Reset the password directly through your provider if there's any doubt.
2. Generate an app password if two-factor authentication is active: Most providers with 2FA enabled require a separate app-specific password for SMTP access rather than your normal login password.
3. Switch to OAuth2 where supported: If your email client supports it, remove and re-add the account, choosing the sign-in-with-provider option rather than entering a raw password.
4. Double-check server settings: Confirm the SMTP server address, the port (587 for STARTTLS, 465 for SSL), and that authentication is enabled.
5. Check for network or server status issues: Try a different network to rule out local connectivity problems, and check your provider's status page for outages.
6. Temporarily disable firewall or antivirus software: If this resolves the error, add a permanent exception for the relevant ports instead of leaving protection off.

Deeper troubleshooting

If the basic steps don't resolve it, a few more advanced checks can help:

• Check for IP blacklisting using a reputation lookup tool if you suspect your sending IP has a poor history.
• Review your email client's connection logs, which often show exactly what was sent and rejected during the handshake, pointing to whether the issue is credentials, encryption, or reputation.
• Update or reinstall your email client if it's outdated and doesn't support modern authentication methods like OAuth2.
• Review your SPF and DMARC records, since misconfigured DNS can compound authentication issues even after login itself is fixed.

Common questions

Is 535 the same error across every provider? The code and general meaning ('credentials rejected') are standardized, but the exact cause and fix can differ slightly by provider.

Should I reuse my main account password as an app password? No — generate a dedicated app-specific password for each client so you can revoke access individually if needed, without changing your primary login.

My credentials are definitely correct — why is it still failing? Check whether your provider has deprecated basic password authentication entirely, in which case no password (correct or not) will work until you switch to OAuth2 or an app password.