Verification email not received by domains using Office365 email client

Question

When someone signs up they receive an email with a link they need to click to verify their email. The email comes from [email protected]

So far all clients receive this email with the exception of clients using their own domain with Office365. With these clients it's not an issue of emails going to spam - they don't receive anything at all in either their spam or their inbox.

The email is sent from a domain that uses Google Business for email.

Any ideas how to solve this issue?

I should add that if the email is forwarded manually, it does come through, just not when automatically sent.