How to verify a live.com email address

Live.com's server replied 550 5.7.1 Unfortunately, messages from [IP] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140).. That refusal happened at the MAIL FROM stage, before the checking server could name any recipient, so it is a verdict on the connecting server, not on the address. SimpleVerifier returns these as risky with "Mailbox check unavailable" and never as invalid, because treating a refusal as "mailbox not found" would delete real customers from your list.

Servers screen connections this way to keep spam out: missing reverse DNS, a low sending reputation or a blocklist listing are the usual triggers. The same screen applies to every checking service that connects from a shared or new IP, which is why live.com results differ between verifiers. SMTP verification false positives explains how much to trust each answer.

Even from a server Microsoft does accept, consumer Microsoft domains don't give a dependable mailbox answer, which is why SimpleVerifier returns them as "Provider hides mailbox status". The Outlook page covers that behaviour in detail.

Treat inconclusive live.com results as unknown, not bad. The checks that don't need the mailbox still work: format, typo domains, duplicates and whether the domain can receive mail. The free list health check runs those in the browser.

For the rest, use the address's history. An address that signed up, bought or replied recently is very likely live. For old or bought data at live.com, send a small batch first and suppress anything that hard-bounces. If the live.com share of your list is small, it's often simpler to keep those rows out of a high-risk campaign than to guess.