Scheduled emails always get blocked by yahoo and gmail #1436

Hello

I'm on the free tier currently. I'm getting this issue when targeting non gmail email addresses.

Email was deferred due to the following reason(s): [IPs were throttled by recipient server]

Edit: I've noticed the following: Yahoo.com and gmail.com block the scheduled emails ie they almost never get delivered to my gmail and yahoo personal accounts (email addresses). The message is this:

The email was not delivered to the recipient. We'll continue trying to send this email for a few more hours, then show a Bounce if it can't be delivered. Learn more.

Latest response from the yahoo.com server:

Email was deferred due to the following reason(s): [IPs were throttled by recipient server]

However for non-gmail-yahoo-addresses eg. cock.li, they do get sent at the scheduled time but they always end up in Spam folder.

Again, I'm on the free tier. Do I have to buy the subscription for 20 USD a month for this NOT to occur?