Dynamics CRM 2016 EMAIL ROUTER: The SMTP server requires a secure connection or the client was not authenticated.

Hello Team,

I setup Dynamics crm 2016 on-premises email router

Everything works fine on the test environment, after the UAT

We change the test environment IP address to working environment IP address

We encounter big challenge with outgoing email,

All the outgoing mail status stock on "Pending Status"

event management gave me an error...

#61042 - An error occurred while processing the outgoing email message with subject "SLA Warning Email UP:0001266" for SMTP: http://crmapp/domain for delivery through smtp.gmail.com. System.Net.Mail.SmtpException: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at
   at System.Net.Mail.MailCommand.CheckResponse(SmtpStatusCode statusCode, String response)

at System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byte[] command, MailAddress from, Boolean allowUnicode)
   at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception)
   at System.Net.Mail.SmtpClient.Send(MailMessage message)
   at Microsoft.Crm.Tools.Email.Providers.SmtpPollingSendEmailProvider.ProcessMessageInternal(Entity emailMessage)

I will appreciate advice, help from anyone

Thanks.