How to Fix “Authentication failed 535 Incorrect authentication data” in Outlook?

Sometimes you encounter an error message such as Authentication failed 535 Incorrect authentication data or SMTP Error (535): Authentication failed when logging into Outlook, or any other email client. One possible cause is because the email password is too weak.

Luckily, the problem can be easily solved. All you need to do is log into your webmail and change the password to a strong and complex password.

A Strong and Complex Password is:

1. A combination of lowercase and uppercase alphabets, numbers (eg: 123) and symbols (eg: &%$#).

2. Not a dictionary English word.

3. Not a number sequences.

An example of a good password is: WQ3xkd&YP2mbz#G93uRq

Performing this change also has the added benefit of securing your email account, lowering the likelihood that your account will be compromised. Once the password has been changed in webmail, be sure to change the password in Outlook as well, which will resolve the error.