SMTP authentication failure while using SendGrid/Gmail

Question

I am getting SMTP Authentication Failure on the server and the mail is getting send via the server SMTP only...

It appears to be a server configuration or related problem, but I am not sure.

This is the debug details:

250-SIZE 52428800
250-8BITMIME
250-PIPELINING
250-AUTH PLAIN LOGIN
250-STARTTLS
250 HELP

Failed to authenticate password. Error: 535 Incorrect authentication data

from: 250 OK

to: 250 Accepted

data: 354 Enter message, ending with "." on a line by itself

250 OK id=1U8Pjp-0002As-FB

quit: 221 ************** closing connection

Your message has been successfully sent using the following protocol: smtp

While testing from my local system, this works and the email is being sent via sendgrid.me

Again, This may not be a SendGrid Problem, but if you have faced similar issue, Can you please tell me what is the problem here?

I am using CentOs and I have cPanel in the server. I believe we are using EXIM for mail server.

Answer 1

For anyone that comes across this in future and are using cpanel/whm, you need to 'disable' this option under 'SMTP Restrictions' in WHM.

Answer 2

I was able to resolve this.

The issue was my server was not allowing the use of external SMTP and using its own SMTP server. I changed the settings and now it works fine.