brain trust: email-routing question

[cellio]

Dear brain trust,

On my domain, I have email addresses that collect a local copy (i.e. I can use webmail on my domain to read them) and also forward a copy to my Gmail address. This is particularly helpful for low-volume addresses that I might not otherwise check frequently.

Today somebody with whom I'd been corresponding contacted me via another channel to report that his email was now being rejected -- by Gmail. Sure enough, the copies are sitting in my domain mailbox just fine, but there's no sign of them at Gmail -- not in trash, not in spam, just not there. Gmail seems to have decided to reject them and not even tell me.

I have questions.

1. How do I get Gmail to stop doing that, at all? If email is sent to my Gmail address, especially by my own forwarder!, I want it to show up there. In the spamtrap is fine if Google thinks it is. Silent deletion is Not Ok.

2. If I can't get Gmail to stop doing it, can I get notifications somewhere?

3. I expected the forwarding from my domain to Gmail to be a private matter between those two parties. Why did the Gmail rejection get all the way back to the sender? Why did I not receive a notice of the rejection at my domain address, which is what sent it along to Gmail? Is there something I can do, presumably via CPanel, to intercept rejections by forwarding addresses?

4. Gmail has filters, which can be used to process incoming email in various ways. I've used them to whitelist a few senders that Gmail thinks are spammers that aren't. When in the pipeline do filters get applied? I think it's after this rejection it's doing, since the message goes nowhere that I can see, but I've whitelisted this particular address now in any case.

Comments

[siderea]

It wouldn't necessarily be anything about how he sends email: if the company(s) he uses in his email system changed a configuration, that can set off Gmail, too. For instance, nobody that uses Gmail has any say about Gmail's SPF, DKIM, or DMARC settings. SPF records are on the level of whole domains and live in DNS, so unless one is sending email from a domain name one controls, one has zero say over its SPF record.