Mails sent from Drupal contact form are blocked

Mails sent from Drupal contact form are blocked

Hi there.

I am using Zoho to host the e-mails for a domain (the domain name is registered elsewhere). I have succesfully set up my first email accounts of the type user@mydomain.org. Everything works just fine.

I now wanted to use one of these accounts (let's say info@mydomain.org) to send mailings from my Drupal website. I have installed the SMTP module and successfully set up the Zoho SMTP server (smtp.zoho.com, port 465, SSL protocol). When I try to send a verification mail to my personal e-mail, it is successful. I also received an automated update alert for one of my modules. So I know that my web server, my Drupal installation and my SMTP settings are properly set up for mailings through my website.

However, a problem arises when I try to use the Contact Form of my website. Invariably, mailings through smtp.zoho.com fail and I get the following errors in my logs:
SMTP Error: Data not accepted.
SMTP server error: Relaying disallowed
I believe this to be related to an issue reported here a year ago.

To verify, that it is a Zoho issue I changed my website's contact information and used a Gmail address with smtp.googlemail.com.

The Contact Form now worked!

So I know it is an issue with the Zoho SMTP server blocking some of my mailing attempts for some reason.

Can that problem be resolved? It is very critical to know that my SMPT server can relay e-mails from my website forms without problem.