I have set up 2 clients on G Suite. According to Google's support, its online tools and everything I know about email delivery, the DNS configuration is perfect: SFP, DKIM, DMARC.
They can send emails perfectly and their emails always arrive.
The problem is that they don't just receive emails for some domains. One is icloud, the other is a large hotel chain and the other is a university.
I contacted Apple Support and after months of trying to reach the right person, they were able to change "something" at the end of it so that email is routed to one of the domains. (But they won't tell me what was going on.)
This is where it gets strange … The client, which can now receive emails from icloud, can ONLY receive on a domain alias. The other domain aliases still don't receive email from icloud or these other senders. Whatever Apple changed in the end only affected that one domain.
Even stranger. If icloud sends an email to email@example.com, it will be forwarded. If you send to firstname.lastname@example.org, it won't go through. If they email both Gmail and CC to the client, won't the email go through? What in the world could be causing this?
I can get the message ID from icloud and GSuite support says that these IDs never reach the server. Since I can't reach IT departments for any of these organizations, I can get error codes or answers. I only have disgruntled customers who do not receive emails from important contacts.