We’ve made some enhancements to our Client Validity Checks filter: configurable envelope address characters and a multi-domain settings mode. Although all 7bit ASCII characters are technically allowed by RFC, many of the uncommon ones are misused by broken mail servers, viruses, and poorly written mass mailers.
If desired, some of the most commonly abused characters may be rejected. You can also add a whitelist rule for Client Validity Checks for trusted sources.
We’ve also added a multi-domain settings mode that’s identical to the other filters that offer this feature so that you can update some or all of your domains without having to waste time configuring them individually.