Thats more or less an argument FOR using one of the large providers. Frankly you are more likely to make exceptions and monitor internally for deliverability f

Thats more or less an argument FOR using one of the large providers. Frankly you are more likely to make exceptions and monitor internally for deliverability from a google, or outlook.com or comcast.net than for some random xyz.email domain. And blocking swaths of those has a bigger impact. Frankly though, imho, you should respond to users that report deliverability issues on your domain and tweak your spam filters accordingly. Just ignoring a users saying "i am not getting expected emails from this listserve" is a great way to encourage your users to employ shadow IT and just use personal accounts. Obscurity isnt security, even with spam mitigations. Things like SPF, DKIM, DMARC along with some user impersonation filtering (including spoofing from fields) is basic spam 101 and will catch 99% of your actual security related phishing.And the largest ones (dmarc) can be probed publicly anyhow since almost all of it relies on DNS txt records.