[exim] Forwarders when using Exchange server

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Author: Charles Pedro
To: exim-users
Subject: [exim] Forwarders when using Exchange server
I have Exchange Server 2016 setup with the same registered domain name in

Exchange Server 2016 Setup
Server Name: SVRA
AD Domain Name: adsvr.com
Full computer name: SVRA.adsvr.com
External Interface IP (public):

cPanel Detail
Registered Domain Name: adsvr.com

Zone Records:
adsvr.com. 14400 IN A (cPanel IP Address)
webmail.adsvr.com. 14400 IN A
autodiscover.adsvr.com. 14400 IN A

adsvr.com. 14400 IN MX Priority: 0 Destination: adsvr.com
adsvr.com. 14400 IN MX Priority: 0 Destination: webmail.adsvr.com

mail.adsvr.com. 14400 IN CNAME adsvr.com
www.adsvr.com. 14400 IN CNAME adsvr.com
owa.mainstreetbankmfb.com. 14400 IN CNAME webmail.adsvr.com

Above are the configuration of the Exchange Server and cPanel Setup
Everything is working. Users can send and receive both internal and
external mails except
mails coming from Gmails/Yahoo (i.e. public mails) are bouncing back.

All email accounts are hosted on the Exchange Server 2016.
Now we want to create forwarder with the following conditions
A. All mails will be access through Outlook Web Access when Exchange Server
is Online
B. Some selected email accounts should access their mails through cPanel
Webmail when the Exchange Server is offline

I tried creating a forwarder like this

Address to Forward: charles@???
Destination Forward to Email Address: charles@ (since I am using
the registered domain name for my Exchange Server 2016)

It worked the first time I created it but some few minutes later, mails are
either bouncing back or stay in the cpanel when Exchange Server is Online.

1. Please How can I achieve scenerios A and B? This is my first priority to
2. How do can users receives mails from public domain?

I have tried changing the Email Routing from Local to Remote inorder to
achieve this, but the mail bounce back to the sender with this error

<charlesa@???>: host adsvr.com[]
    said: 550-Please turn on SMTP Authentication in your mail client.
    550-sub5.mail.dreamhost.com (homiemail-a140.g.dreamhost.com)
    550-[]:58381 is not permitted to relay through this
    550 without authentication. (in reply to RCPT TO command)

I am just wondering if I could include an MX record for the localhost A
record on the cpanel so that the mail can be routed to the cpanel mail
server if the remote is offline.

What is the function of the localhost with IP on the cpanel?

How do I route the mail to the cpanel since I have set the Priority of the
MX records as follows:

adsvr.com. 14400 IN MX Priority: 0 Destination: adsvr.com
adsvr.com. 14400 IN MX Priority: 0 Destination: webmail.adsvr.com

Or what does this error mesage implies? I have both account (i.e.
charles@???) created on the cpanel as well as on the exchange server.


Charles Pedro