A security token is an alpha numeric code that you need to append to your password when you login to Salesforce. Note that it is case sensitive. You will need one in case you login using an API or a desktop client that has an IP address outside of the trusted range specified by your organization.
Where to Find Your Security Token
Whenever you reset your password, the system will send you a new security token via email. Some security token values will be created by an authenticator app. An example of which is the Salesforce Authenticator.
Note that there are client applications that will require you to enter your security token on a separate field. If that extra field isn’t provided then that means you will need to add your security token in the same field where you enter your password. You just have to add it or append the code at the end.
Security Tip: Do not use your security token when logging into Salesforce via a browser.
Resetting Your Security Token
As stated earlier, you can reset your security token in Salesforce when you reset your password. However, you can also reset your security token using a separate process.
You should start at your personal settings. Go to the Quick Find box and enter “Reset.” Select Reset My Security Token in the options. After you click that, a new security token will be sent to your personal settings. You will also receive an email confirming the reset and you will see the new security token there.
After resetting your security token, remember to update this info on Outlook. Go to tools > Salesforce options. Enter your password with the security token appended to it and then click Verify. Click OK.
Note: You will get an error when entering your password with the security token appended if you login with an IP in your organization’s trusted range.