How to route mail (Dovecot, Postfix setup ) to Office 365 - same domain

Hi to all,

This is my very first post and I think is a good chance to express my gratitude and satisfaction with DO services and great community support.

I have setup a working Linux mail server on my DO droplet, however recently, I have decided to switch over to Office 365 subscription and updated my DNS tables records to forward MX for my domain to Microsoft Exchange servers.

Everything was successful and now it was deployed in production.

On my Droplet webpage there is a contact mail form for visitors, which sends email to mailbox accounts registered on my droplet mail server.

Same mail accounts boxes are already setup in Office 365, however the problem is that all messages sent form the webpage mail form are routed locally - only on the droplet mail server itself since the domain name and mail accounts are both identical on my Linux box and Office 365 .

My setup:

On the Postfix server and Office 365 I have:

alias - hostmaster@example.com forwarded to user1@example.com user2@example.com user3@example.com

Is there a workaround to actually force Postfix to send the messages to external Exchange server given the fact that both servers are sending mail for example.com

Your valuable advise and support would be highly appreciated.

Thanks