No verification code when external recipients access shared secure links

Hello,

I have a user that is experiencing the issue outlined in the URL below where the receiver of the OneDrive/SharePoint shared files/folder emails don't receive the code and says it's not showing up in their junk email mailbox. Any ideas on what I can check beyond that? I don't think this is something on the sender side but the receiver side. I tested with my own account and was able to get the code just fine. 

https://docs.microsoft.com/en-us/sharepoint/troubleshoot/sharing-and-permissions/no-verification-code-to-access-shared-secure-link