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Why are iCloud, Outlook and Hotmail addresses not always valid?
Large providers often do not give a clear answer to a mailbox check. The result can then be unknown, risky or less certain than for a company domain, even when the mailbox is real.
ValidReach Team · Updated 2026-10-26
What you will see
Often unknown, which is not billed. Retry later, since a temporary refusal may clear.
What to do
Treat these addresses as a separate segment. If they matter, use a confirmation email to prove they work.
Why
Providers protect users from address harvesting, so they restrict what a stranger can learn about a mailbox. Verification is limited by what the server tells it.
Good to know
This describes the method, not a defect of one provider. Behaviour changes over time, so retest if it matters.