I have been given another E-Mail domain used by another company I am a part of however they do not use Office 365.
They will not change their mailserver but will allow DNS changes as long as it does not effect their own mailflow. They are simply setup with a cPanel hosting account for a mailserver.
I want to know if the following is possible to setup:
My current E-Mail address in Office 365: email@example.com
My other E-Mail address hosted externally: firstname.lastname@example.org
The other E-Mail address does not support active sync and only supports POP3 and IMAP. The goal is to not require 2 accounts to be setup on all my devices. I can make all E-Mails redirect from the theircompany.com address to my own address but I need to be able to send out as me@ theircompany.com as well.
So my main question is:
1. Setup an initial txt record on the new domain to validate the ownership of the domain to O365.
2. Then add the me@ theircompany.com address as another account of email@example.com in O365.
3. Then setup full rights to me@ theircompany.com for firstname.lastname@example.org so that I can use my O365 account to send out as email@example.com
There could therefore be no mx record changes to the other domain.
Would I then add an spf record for the other domain to allow E-Mails to be sent from O365 as well as their mailserver?
Will any of that work? If not how could I set this up?