When it comes to email, nothing is more essential than communication—especially when money is to be made—and emails need to be sent and received in the fastest, most efficient way possible. While email functions over many general protocols, the vast majority of sending and receiving email across disparate servers falls under the Simple Mail Transfer Protocol (SMTP). Yet there is one important aspect of SMTP that does not apply—transfers mistakes that come from larger endeavors via one-time transmission—business or personal.
Among your potential frustrations, SMTP Email Error 535 5.7.3 is one of the most common. This particular SMTP email error is usually related to authentication errors—meaning the system is not convinced who is trying to send what at the moment. Ultimately, this means mail cannot be sent, and important correspondence that should be sent will not be sent—causing problems with client relationships and stalling internal operations. Understanding what this error code means and how you can fix the problem will ensure your email operations stay on the up and up.
SMTP Error 535 5.7.3 essentially means that your email wasn’t sent because the server can’t authenticate the sender. While the error notification message differs from program to program, the general user experience is one of an “Invalid Authentication Credential” or “Authentication Failed.” For example, Microsoft Outlook says “Error 535 5.7.3 Authentication unsuccessful,” while Apple Mail says, “Cannot send mail. The username or password for [SMTP server] is incorrect.” The Email SMTP Error 535 5.7.3 relates to authentication.
Authentication is a form of security verification that guarantees a user has permission to send correspondence through the specific mail server. Therefore, when, for example, the email program on the host machine creates these necessary credentials for authentication and the server denies them, an error is generated. The server denies them for several reasons; someone may have changed their password, someone may have implemented new layers of security, or the application does not acknowledge the default security measures acknowledged by the server.
Related – Understanding and Fixing the SMTP 535 Error: Incorrect Authentication Data
Primarily, SMTP email error 535 5.7.3 occurs when there are issues with the authentication process of the server required to send emails. Below are some possible causes that could lead to error 535 5.7.3.
- The first common error message that appears is “using invalid credentials.” This implies that the log-on is wrong—however, it is, with password and ID. The causes for this error message are that either some sort of typo happened, a password change has not propagated yet through the email client, or the email user used to have the access but does not anymore, and the old credentials do not comply with the new server security settings.
- The second reason behind error 535 5.7.3 is misconfiguration. Another reason for server authentication errors is misconfiguration. For instance, where the email client configured doesn’t match what’s really valid, e.g., the SMTP server needs proper authentication and fails because the server-port configurations are wrong.
- Another error generated by the recipient is 5.7.3. “Publisher security update.” This means that something changed on the publisher/email service provider’s end in security or the authentication it offers. Should the email recipient fail to follow the dictates of what’s been published—meaning, if it stays at a less secure authentication when the more secure authentication is now required—this is the response it receives for noncompliance: 535 5.7.3.
- Another cause is the “Account Lockout” phenomenon. This means that the email host server might lock the accounts if it registers suspicious activities or when a breach has occurred. When the service provides files that there is no warning, the client receives the 535 5.7.3 error.
- Finally, the cause is “Software conflict” whereby the email client installed uses outdated software that no longer complies with the server’s settings or software with no updates will encounter the 535 5.7.3 error.
- Verify Password and Username. Verify that the username and password in your email client are current and accurate. Update your Gmail password in your email client as well, if you’ve changed it recently.
- Enable Less Secure Apps (if necessary). You might need to enable “Less Secure Apps” in your Gmail settings if you’re using an older email client. Nonetheless, using email clients that support OAuth is advised.
- Verify SMTP Settings:
- SMTP Server: smtp.gmail.com
- Port: 587 for TLS/SSL
- Authentication Required: Yes
- Username: Your full Gmail address
- Password: Your Gmail password
- Update Password. Ensure your password is correct, especially if you have recently changed it.
- Check SMTP Settings:
- SMTP Server: smtp-mail.outlook.com
- Port: 587
- Encryption Method: STARTTLS
- Authentication Required: Yes
- Username: Your full Outlook email address
- Password: Your Outlook password
- Password Verification. Confirm that the password and username are correctly entered in your email client.
- Adjust SMTP Settings:
- SMTP Server: smtp.mail.yahoo.com
- Port: 587
- Encryption Method: STARTTLS
- Authentication Required: Yes
- Username: Your full Yahoo email address
- Password: Your Yahoo password
- Confirm Authentication Details. Double-check your username and password. Reset your password if unsure and update the new password in the email client.
- Correct SMTP Settings. Refer to your email provider’s help documentation for the correct SMTP server settings, including server address, port, and encryption method.
- Contact Support. If you continue to have issues, contact your email provider’s technical support for guidance on specific settings.
SMTP Email Error 535 5.7.3 workaround may become harder and harder to find; however, Warmy.io can help. Warmy.io is a service that slowly boosts your sending reputation based on all emails you’ve ever sent—you’re basically warming up your sending history—so you’re seen as a legitimate sender by countless email servers to avoid any ceiling caps from sending your emails to spam. In addition, Warmy.io improves all elements of your emailing reputation via their email deliverability and blacklisting checks, for example. Warmy.io has free SPF and DMARC record generators to guarantee that you properly authenticate your emails on your end, which helps avoid these issues on the receiving end. Likewise, Warmy.io helps provide excellent email deliverability for your domains and prevents any SMTP errors that would hinder successful communication.
The need for troubleshooting SMTP error 535 5.7.3 is essential and could mean hours upon hours of lost productivity and lost confidence in email. The error prevents you from being able to send email, which jeopardizes friendships, fails to impress potential employers, and puts one’s professional reputation at risk. Therefore, troubleshooting this issue and understanding proper configurations of the email settings is necessary for any kind of extended use; it makes communication efficient and safe. Email configurations to avoid threats are essential; they make your email clearer and more deliverable when on the back end it’s cleared up with relative frequency. It’s only a matter of time and effort for the benefit of having access to a safe and secure means of communication.
📜 Related article:
What is SMTP Email Error 535 5.7.3?
When an email client provides the SMTP server with erroneous or unaccepted login credentials, the SMTP email error 535 5.7.3 arises, prohibiting email from being sent.
What is the reason of SMTP Email Error 535 5.7.3?
This error usually occurs when the SMTP server's authentication procedures are incorrectly setup, the username or password is entered incorrectly, or the account security settings are altered.
How can I resolve my email client's SMTP Email Error 535 5.7.3?
Make sure the right username and password are entered in your email client's settings to fix this error. Additionally, confirm that the authentication criteria of your email provider haven't been altered. It can also be beneficial to change your password in your email client and reset it.
Does SMTP Email Error 535 5.7.3 get fixed by changing the SMTP port?
This problem usually cannot be fixed by changing the SMTP port on its own unless there is a specific port misconfiguration involved. Since authentication is mostly the cause of this problem, pay close attention to your security settings and appropriate credentials.
Can I repair the problem by updating my email client software?
It's true that occasionally underlying problems that could be producing login difficulties, like Error 535 5.7.3, can be fixed by updating your email software. Ensure that the most recent security and functionality updates are installed in your email client.
How can I tell if the security settings on my email server are the reason for SMTP Error 535 5.7.3?
To find out whether there have been any changes to the security or authentication policies that might be affecting your ability to send emails, see the documentation or assistance provided by your email service provider.
