[jeroenhd]

I have seen something similar at a smaller ISP, but the silently discarded email usually came from domains with bad SPF setups.

Really infuriating, because customers would not believe that this wasn't a problem on our end, it was the other side telling us to discard their email!

[CodeWriter23]

You wanna know what's worse? There is an SPAM Scoring Monoculture, dominated by BrigthWorks, Symantec and another firm that escapes my mind right now. So if users flag enough of your email as Junk on an ESP using one of these providers, your domain is banned or auto-Junked with all that company's other customers.

[Avamander]

SPF alone is not a reason for discarding a letter.

[jeroenhd]

It shouldn't be, but the standard is not clear.

The spec is very dodgy in that it acknowledges that every server needs to pick its own policies:

> Disposition of SPF fail messages is a matter of local policy.

On silently dropping email, the following is listed as a "consideration":

> Other dispositions such as "dropping" or deleting email after acceptance are inappropriate because they leave uncertainty and reduce the overall reliability and utility of email across the Internet.

There is no MUST (NOT) in the spec when it comes to silently dropping email.

The intent of the author of the spec is to always provide feedback, but it doesn't actually say that in cleae terms.