Email/Exchange “that domain isn’t in my list of allowed rcpthosts”

I work with an organization which hosts its own email. Very occasionally,
we receive the following message when sending an email to only 1
particular address outside our organization. To resolve, we can log onto
the server, access the website of the recipeint domain, then resend the
email and it will go through. I suspect this is a DNS issue, but I am
cannot figure out where to search for clues. I have searched using the
Excahnge Manager tand traced the email that generated the NDR, and it
seems the Mail never leaves our system. But when it works it passes
several hops then lands correctly at the recipients domain. Any ideas?

thanks so much all!