The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required.

Error:

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required.

Solution:

This generally happens when you try login from different time zone/IP/Computer. You production server and the mail id you have used both are in different time zone. Choose any of the one solution:

1) Log in to production server via remote access, and sing in to gmail once with your credentials. They will ask for the confirmation, confirm it and log out.

Or 2) log in gmail to your local computer, 

Blocked sign in notification

If you receive a notification that we prevented someone from signing in to your account, it means we blocked an attempt to access your account because we weren’t sure it was really you. The password was correct, but we didn’t recognize either the device or the location. To help protect your account, we ask you to visit the Devices & activity page to let us know if this was you.

Review the suspicious sign in

When you click the link provided in the notification, we’ll take you to a page with more details about the suspicious sign-in at the top. Here are a few details to review to help determine whether or not the sign-in was yours:

• Device: Is this a device you own or recognize?
• Time: Do you remember trying to sign in to this device at the date and time listed?
• Location: Do you remember signing in from this place?
• IP Address: Is this an IP address you recognize?
• Browser: Is this a browser you usually use?