Laravel - Sending Emails Through Exchange Server

For my Laravel 5.1 app, I have an on-premise Exchange server and user account that I want to sent emails through. Below are the values in my .env file:

MAIL_DRIVER=smtp
MAIL_HOST=[IP ADDRESS]
MAIL_PORT=587
MAIL_USERNAME=[USERNAME]
MAIL_PASSWORD=[PASSWORD]
MAIL_ENCRYPTION=null

I get an error when using tls as the encryption value and just for the sake of testing, I've been using null for now. But then I get the error of Failed to authenticate on SMTP server with username "*******" using 1 possible authenticators

I'm unsure of where I should start for troubleshooting. It seems that it's using NTLM Authentication for verifying the credentials. Should I check the Exchange server to see if it's set up for that? The credentials I used are correct. Or is there something wrong with my config?

Thanks in advance.

via Chebli Mohamed