Emails aren't being received by Outlook accounts

I am extremely new to Cloudflare and DNS setup, so bear with me. I have also searched online for any duplicates and couldn’t find anything similar to mine. That and the answers were not very clear to me.

Cloudflare is preventing emails to be received to all Outlook accounts. I am a developer and have done multiple tests on my local and on Pantheon (where the site is hosted). No issues on my local since it’s not attached to Cloudflare. However, when I’m on Pantheon (Cloudflare is attached), the emails won’t arrive. I can see that they are being sent out via the Gmail SMTP that I have set up. But when I check my Outlook email account, I don’t have the email. Works fine when testing with a Gmail account.
I have tried multiple versions of MX records and I can’t seem to find the correct combination. Please, assist.

Thanks.

Could you post the domain? Us being able to see your domain’s DNS setup is extremely helpful.

In general you should check to see if you’re just unable to load email via outlook, or if the email isn’t being delivered. If you get a “email undeliverable” email back, then chances are the MX setup isn’t correct. If the email goes through, but you just can’t see the email in outlook, chances are the connection to Outlook is being blocked.

I’ll check with my supervisor tomorrow morning and get back to you.

But based off your second paragraph, it sounds like Outlook is blocking it. How would I verify it?
More on the situation: I am using Swiftmailer (module for Drupal 7), which is configured to use SMTP with a Gmail account. When I send out a test email to another Gmail account, the email is received. When I send out a test email to a Outlook account, the email is not received. However, the Gmail account used for SMTP shows that both emails have been sent (no “email undeliverable” message, etc). So Outlook does seem to be blocking? On top of that, I have logged into the Gmail account that is being used for SMTP and sent an email to the Outlook account without the SMTP setup and the email arrives.