Workflow
Warm-up vs email verification
Warm-up addresses the sender; verification addresses the recipient. A warmed mailbox still bounces if you send to bad addresses.
What each fixes
Warm-up works on how a mailbox is treated over time. Verification removes addresses that cannot receive mail, which cuts hard bounces whatever the mailbox history.
Using both
Do both and compare which one moved your numbers: bounces point at the list, placement problems at the sender. Inbox placement is not promised by either.
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