If you use Gmail SMTP, then follow the below steps:

Step 1: You have to Click here and select Turn ON Access for less secure apps.

Step 2: Provide the below details and save it.

Smtp Server : ssl://smtp.gmail.com

Smtp Port : 465

Smtp Username : Gmail address

Smtp Password : Gmail login password

Note: Still having difficulties in Gmail SMTP integration?

Please Click here and allow access to google accounts for security purpose by clicking on the Continue button

Kindly disable the 2-step verification and then do the Step 1 and step in the Note

To enable/disable the 2-step verification, Click here and then Turn off the option