Right, and this is exactly why they need to reject. At least the sender would know and could try to contact the receiver to let them know Gmail/outlook is blocking them.

Right now, when you send an email, you don't know if it was received or not and if the lack of answer is a conscious decision or because of filtering.

You can blame the spammers for that.

Do you remember the bad old days of spam?

Left unchecked I think it might have destroyed the e-mail ecosystem entirely.

Regarding the block vs reject, that unfortunately gives a big tip to the people whose working hours are spent trying to defeat three blocks and send you more spam.

Yes I remember, but this was a different world, it was a world without reputation networks, without ip black lists, with SPF/DKIM.

There is not reason at all to suspect that a message from a small server with proper SPF and DKIM that has never sent spam (for real or spoofed, see SPF), is spam. The other half is from small servers that sprung over night and have no reputation.

Half of the spam I receive is from google/outlook/amazon. They don't block each other, do they?