Mailbox provider · mailbox.org
How to verify a mailbox.org email address
Can you verify @mailbox.org addresses?
YesYes. @mailbox.org answers mailbox checks one address at a time.
Check one address
Five checks a minute, no account needed. Nothing is sent to the address — we ask its mail server whether the mailbox exists, then disconnect.
Checking a whole list? The first 100 addresses are free, with results to download. No card.
By continuing you agree to our Terms and Privacy Policy.
The checker opens an SMTP conversation with mailbox.org's mail server, offers a random address first to rule out a catch-all, then names your address at RCPT TO and disconnects without sending. A rejection comes back invalid ("Mailbox not found") and an acceptance valid ("Mailbox exists"). Temporary replies come back risky. It always checks the syntax, the domain's MX records, disposable domains and role addresses such as info@ first.
Mailbox existsMailbox not foundServer would not confirmmailbox.org addresses can be verified without sending an email. On 4 November 2026 the mailbox.org mail server mx2.mailbox.org rejected a made-up recipient at the SMTP RCPT TO step with 550 5.1.1 <…@mailbox.org>: Recipient address rejected: User unknown in relay recipient table, so a mailbox check can tell a missing mailbox.org account from a real one.
Price: this tool is free. Checking a whole email list is from $9/mo, and the first 100 checks are free with Google, no card. See pricing
Live DNS snapshot: mailbox.org
Checked 5 November 2026, 03:29 UTCRead from DNS at the time shown and refreshed at most once a day. MX says where mail for mailbox.org goes; SPF and DMARC describe mail sent from it, not whether any one address exists.
- 10
mx2.mailbox.org - 10
mx4.mailbox.org - 10
mx1.mailbox.org - 10
mx3.mailbox.org - 50
mx-n.mailbox.org
v=spf1 ip4:213.203.238.0/25 ip4:195.10.208.0/24 ip4:91.198.250.0/24 ip4:80.241.56.0/21 ip6:2001:67c:2050::/48 mx ~allp=reject: meets the requirement and enforces it.
v=DMARC1; p=reject; adkim=r; aspf=r; pct=100; rua=mailto:abuse+arf@heinlein-support.de; rf=afrf; fo=1;Look up any other domain with the MX lookup or the email provider lookup.
mailbox.org at a glance
| Operated by | Heinlein Support GmbH, Berlin, GermanySource: mailbox.org general terms, section 1 |
|---|---|
| MX hosts | mx1.mailbox.org, mx2.mailbox.org, mx3.mailbox.org, mx4.mailbox.org, mx-n.mailbox.orgObserved 4 November 2026 (dig MX) |
| Answer to a made-up address | 550 5.1.1 <…@mailbox.org>: Recipient address rejected: User unknown in relay recipient table, returned at RCPT TOObserved 4 November 2026 (SMTP probe of a made-up recipient, no message sent) |
| Address rule | A cancelled account's address stays blocked before anyone can register it again: 90 days on Light, at least 1 year on Standard, at least 2 years on PremiumSource: mailbox.org KB: when is a deleted address available again? |
| Address rule | Standard and Premium plans can create, delete and recreate up to 25 aliases on the @mailbox.org domainSource: mailbox.org KB: email aliases |
| Inactive accounts | All data of a closed account is irretrievably deleted after a 60-day retention periodSource: mailbox.org general terms, section 10 |
What mailbox.org's server says about a missing mailbox
The reply that matters is the one to RCPT TO, the step where the checking server names the recipient. mailbox.org answered our made-up mailbox.org address with 550 5.1.1 <…@mailbox.org>: Recipient address rejected: User unknown in relay recipient table. A 5xx code at that step is a permanent "no such mailbox", which is the same answer a real message would get, so SimpleVerifier marks the address invalid with the reason "Mailbox not found". A 250 at the same step means the mailbox exists and comes back valid.
Before trusting a "valid", a careful verifier also offers a random address that cannot exist. mailbox.org rejected ours, so mailbox.org is not a catch-all: a 250 for your address is a real signal. Temporary 4xx replies (421, 450, 451) are about the connection, not the mailbox, and come back risky with "Server would not confirm" rather than invalid. Hard bounce vs soft bounce explains why that split matters.
mailbox.org is paid, and addresses are held before reuse
mailbox.org is a paid service: the terms close an account whose paid period runs out and delete all its data after a 60-day retention period. Its knowledge base says a cancelled address stays blocked for 90 days on Light, at least a year on Standard and at least two years on Premium before someone else can register it.
Users on Standard and Premium can create and delete up to 25 aliases on @mailbox.org, so one person may appear under several addresses, and a deleted alias starts bouncing while its owner is still reachable. The server rejects unknown users at RCPT TO, so a check gives a clear answer for each alias.
Cleaning mailbox.org addresses on a list
Because mailbox.org answers honestly, mailbox.org is one of the domains where verification removes bounces before they happen. Drop the invalid results, keep the valid ones, and re-check the risky ones later: a temporary reply on one day often turns into a clear answer the next.
A valid result only means the mailbox exists today. Addresses on an old consumer list go stale as people stop using them, so re-verify before each large send to an aged segment; how often to verify an email list gives a schedule. Upload the CSV to the verifier and download the valid, risky and invalid rows as separate files.
Common questions
- Can you verify @mailbox.org addresses?
- Yes. @mailbox.org answers mailbox checks one address at a time. The checker opens an SMTP conversation with mailbox.org's mail server, offers a random address first to rule out a catch-all, then names your address at RCPT TO and disconnects without sending. A rejection comes back invalid ("Mailbox not found") and an acceptance valid ("Mailbox exists"). Temporary replies come back risky. It always checks the syntax, the domain's MX records, disposable domains and role addresses such as info@ first.
- Can I check if a mailbox.org address exists without emailing it?
- Yes. A verifier connects to mailbox.org's mail server, names the address at the RCPT TO step and disconnects before sending. On 4 November 2026 the server rejected a made-up mailbox.org address with "550 5.1.1 <…@mailbox.org>: Recipient address rejected: User unknown in relay recipient table", so a missing mailbox shows up as invalid and the owner receives nothing.
- What mail servers does mailbox.org use?
- On 4 November 2026, mailbox.org published these MX hosts: mx1.mailbox.org, mx2.mailbox.org, mx3.mailbox.org, mx4.mailbox.org, mx-n.mailbox.org. You can look them up yourself with the free MX lookup tool.
- Why did a mailbox.org address come back risky instead of invalid?
- Risky means the server didn't give a permanent answer during the check, usually a temporary 4xx reply or a timeout. It isn't proof the address is bad. Check it again later; mailbox.org gave a clear rejection for a missing mailbox when we tested it.
Related tools
Another provider? See every mailbox provider and what our checker does at each.
Got a list with mailbox.org addresses?
Sign in with Google and the first 100 addresses are checked free: valid, risky and invalid, with the reason for each row and a file to download. No card. After that, plans start at $9/mo for 2,500 emails a month.
By continuing you agree to our Terms and Privacy Policy.