Not able to configure "Send mail as" On Gmail

[Sumesh1980]

Hello, 

I want to configure Gmail (using their "Send mail as:" feature) to send mails through my business Office365 Outlook account, , but when I try to connect it I get an Authentication failed message from the Office 365 server with an error message like this:

Authentication failed. Please check your username/password.
Server returned error: "334 VXNlcm5hbWU6 334 UGFzc3dvcmQ6 535 5.7.3 Authentication unsuccessful [SN6PR01CA0011.prod.exchangelabs.com] , code: 535"

I can sign in to Outlook Web App without problems using the same credentials.

Below is the screenshot for the same 

Can some help me to fix this issue 

[#2]

Hola, Office 365 con SMTP usa STARTTLS para autenticar, creo que en Gmail debes usar la opción de SSL.
Espero te ayude.
Saludos.