| Gmail | |
|---|---|
| Domains | gmail.com, googlemail.com |
| Mail routing | gmail-smtp-in.l.google.com plus four numbered backups at alt1 through alt4. The same hosts serve googlemail.com, which is an alias rather than a separate service. |
| What we can resolve | We resolve some mailboxes here |
How Gmail answers a probe
What the server does when we open a connection and ask about one address.
- A live address returns 250 at RCPT TO and nothing else happens. Google does not leak whether the account is dormant, suspended or over quota at this stage.
- A dead address returns 550-5.1.1 with the phrase "The email account that you tried to reach does not exist" and a link to a support page. That string is stable enough to parse.
- Probe from an address range Google dislikes and you get 421-4.7.0 instead, which says nothing about the mailbox. A verifier that scores that as invalid is inventing data.
- Google also applies per-connection rate limits that tighten as the hour goes on. The first few hundred probes behave differently from the next few thousand.
The part that catches people out
What we do about it
We normalize Gmail local parts before the probe, which removes the duplicate rows at no charge, and we treat a 4xx from Google as unknown rather than guessing. When the connection is refused outright we say the probe was blocked and leave the verdict open.
Sending to Gmail mailboxes
Verification is one step. These are the things that decide whether the message lands.
- Since February 2024 anyone sending more than 5,000 messages a day to Gmail needs SPF, DKIM, DMARC, one-click unsubscribe and a spam complaint rate under 0.3%.
- Google Postmaster Tools is the only place you see Gmail's own data on your mail, such as spam rate and compliance status, and it needs a verified domain plus enough volume to report anything.
- Gmail weighs engagement more heavily than most providers. Addresses that exist but never open are a deliverability problem no verifier can find for you.
The underscore that never reached Google
Say you export 6,200 signups from a webinar form and 2,480 of them end in gmail.com. Before any server gets asked anything, read the local parts. Google's sign-up form allows only letters, numbers and periods in a Gmail username, and it asks for 6 to 30 characters. That means jen_park@gmail.com and mike-t@gmail.com almost certainly were never issued to anyone. Somebody typed them wrong, or typed them on purpose to get past your form.
You can catch those rows with a one-line rule and spend nothing on them. The same trick doesn't work for a misspelled domain. Addresses at gmial.com or gmai.com belong to a different domain entirely, and many look-alike domains are registered and do accept mail, so an MX check alone won't flag them. A typo list handles those better than DNS does.
Why a Gmail rejection stays true
Google says a deleted Gmail username can't be registered again, by you or by anyone else. That makes a 550 from Gmail unusually durable. At providers that hand old names to new owners, an invalid row can turn valid again under a stranger. Here it won't, so you can suppress the address for good and skip the re-check.
Valid results age in the other direction. Since December 2023 Google has been deleting personal accounts that go two years without a sign-in, and the policy covers consumer accounts, not Workspace ones. If a segment of your list hasn't opened or clicked since 2023, some of those mailboxes have likely been removed since you last verified. Re-run that segment before a win-back campaign instead of trusting an old clean result, because the first send to a pile of deleted accounts is exactly the bounce spike Gmail's filters notice.
Questions people ask
Can you verify a Gmail address reliably?
Usually, if the probe reaches Google from an IP they accept. Gmail does return a distinct rejection for addresses that do not exist, which is more than several large providers offer. The failure mode is not a wrong answer, it is no answer at all when the connection is blocked.
Why did a Gmail address come back as unknown?
Almost always because Google answered 421 or dropped the connection instead of judging the address. That is a statement about our IP reputation and their rate limits, not about the mailbox. We report it as unknown and do not bill it.
Do dots in a Gmail address matter?
Not to Google. j.smith@gmail.com and jsmith@gmail.com deliver to the same inbox. They matter to your list, because both rows will be billed by a verifier that does not normalize them first.