The fastest way to wreck a sending domain is to mail everyone, every time, regardless of whether they open. The people who never engage drag your reputation down, the mailbox providers notice, and soon even your best customers stop seeing you in the inbox.
Send to intent, not to everyone
Smart Sending holds a fatigue window on every contact, so a person who was just emailed is not hit again inside that window by the next campaign or flow. The people ready to hear from you get the message. The rest are held and released later instead of being burned through.
A held email is not a deleted one. It waits and goes out when the window clears, so a one-email flow never silently drops the only message it had to send.
Quiet is a feature
Sending less, to the right people, is what lets you keep sending at all. A domain that stays clean this month is a domain you can still reach the whole list from next quarter.