Problem: 

• You have your domain hosted with 3Essentials... for discussion, we'll say your domain name is "domainA.com"... but you have your mail for domainA.com hosted elsewhere, perhaps with your own corporate mail server, your ISP, or some other provider.   This means you'd have your MX records pointing to someone else besides 3Essentials.
• You have code on your webpage that needs to send out mail to someuser@domainA.com, but the mail is not arriving.

Resolution:

We host our mail services on the same server as the web server.  So if you have webcode sending to domainA.com, it will deliver it to the mail domain LOCALLY on our server, and never look up the MX record to route it to the correct destination.  

Note that this will ONLY affect mail going to someone@domainA.com... mail you send from your webpage to any other internet email address would be routed correctly... only mail to domainA.com will be affected, because it finds the postoffice for domainA.com on the local server where the webpage tried to send the mail... so it never goes thru the standard MX record look up for mail routing. 

To solve this, we need to DISABLE your mail domain on our server... this allows our mailserver to then properly check DNS for an MX record, and find that it needs to route mail out to the correct internet location... HOWEVER, this then means you can't create an address like someone@domainA.com on OUR servers to use to SEND the mail in the first place, and you MUST have a user like this, as we require SMTP-auth (the usage of a mail user and password to send mail). 

In this scenario, we can create a specific purpose email address for you on our mail domain, like domainA.com@web18.3essentials.com.  You can also tell us to specify a different "reply to" address when we create this account, for example (ourcompany@domainA.com) .  We can make it anything like domainA-mailer@web18.3essentials.com, or domainA.com@web18.3essentials.com, but it must include your domain name as part of the domain. 

ALSO, you will need to have our Plesk control panel has the MX records pointing to the correct location for where you host your mail... EVEN if you have your DNS hosted elsewhere... we need our internal DNS to have the correct MX records.  To make this change, log into the control panel, click on the domain, click on DNS, and then remove the current MX records (which point to 3Essentials mailgateway servers), and add back in the correct MX records to point to your current mail hosting provider.  

With these two steps, the following will work properly:

1. your mail form on our server connects to our mail server to send the mail to your domain
2. the mail server will NOT find the domain is hosted locally, and will look for the MX record
3. it will find the correct MX record (because you've updated our DNS to have the proper MX records)
4. and the mail will be properly routed to your current mail service provider for your domain.

If you have any questions or need further clarification, please feel free to submit a support request.