Mailbox provider · Posteo
How to verify a posteo.de email address
Can you verify @posteo.de addresses?
YesYes. @posteo.de answers mailbox checks one address at a time.
Check one address
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The checker opens an SMTP conversation with posteo.de'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 confirmPosteo addresses can be verified without sending an email. On 13 October 2026 the posteo.de mail server mx01.posteo.de rejected a made-up recipient at the SMTP RCPT TO step with 550 5.1.1 <…@posteo.de>: Recipient address rejected: User unknown, so a mailbox check can tell a missing posteo.de account from a real one.
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Live DNS snapshot: posteo.de
Checked 6 November 2026, 11:12 UTCRead from DNS at the time shown and refreshed at most once a day. MX says where mail for posteo.de goes; SPF and DMARC describe mail sent from it, not whether any one address exists.
- 10
mx04.posteo.de - 10
mx02.posteo.de - 10
mx01.posteo.de - 10
mx03.posteo.de
v=spf1 ip4:185.67.36.0/23 ip6:2a05:bc0:1000::/47 ~allp=none: meets the requirement, but blocks nothing. No rua= address, so you get no aggregate reports.
v=DMARC1; p=none; sp=quarantine; adkim=s; aspf=sLook up any other domain with the MX lookup or the email provider lookup.
Posteo at a glance
| Operated by | Posteo e.K., Berlin, GermanySource: Posteo imprint (German) |
|---|---|
| MX hosts | mx01.posteo.de, mx02.posteo.de, mx03.posteo.deObserved 13 October 2026 (dig MX) |
| Answer to a made-up address | 550 5.1.1 <…@posteo.de>: Recipient address rejected: User unknown, returned at RCPT TOObserved 13 October 2026 (SMTP probe of a made-up recipient, no message sent) |
| Address rule | Posteo addresses can use posteo.de, posteo.com, posteo.net, posteo.us, posteo.ca and several other country domains; aliases can use a longer list of posteo domainsSource: Posteo help: available domains (German) |
| Address rule | Aliases are included (3 per mailbox, more at extra cost) and unlimited filter addresses of the form [email protected] are supportedSource: Posteo services page (German) |
| Inactive accounts | If payment is two months behind, sending is blocked and Posteo then terminates the contract; Posteo deletes stored data 90 days after sending a terminationSource: Posteo terms, sections 4.5 and 9.3 (German) |
What Posteo'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. Posteo answered our made-up posteo.de address with 550 5.1.1 <…@posteo.de>: Recipient address rejected: User unknown. 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. Posteo rejected ours, so posteo.de 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.
Posteo is paid, so addresses lapse through unpaid fees
Posteo charges for mailboxes. Under its terms, a customer two months behind with payment has sending blocked and is then terminated, and data is deleted 90 days after termination. Unpaid mailboxes are the usual way a @posteo.de address goes dead.
One mailbox can answer on many domains. Posteo's domain list includes posteo.com, posteo.net and posteo.us, and its services page mentions +tag filter addresses. The same person can appear on your list under several spellings, so deduplicate by mailbox where you can.
Cleaning posteo.de addresses on a list
Because Posteo answers honestly, posteo.de 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 @posteo.de addresses?
- Yes. @posteo.de answers mailbox checks one address at a time. The checker opens an SMTP conversation with posteo.de'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 posteo.de address exists without emailing it?
- Yes. A verifier connects to Posteo's mail server, names the address at the RCPT TO step and disconnects before sending. On 13 October 2026 the server rejected a made-up posteo.de address with "550 5.1.1 <…@posteo.de>: Recipient address rejected: User unknown", so a missing mailbox shows up as invalid and the owner receives nothing.
- What mail servers does posteo.de use?
- On 13 October 2026, posteo.de published these MX hosts: mx01.posteo.de, mx02.posteo.de, mx03.posteo.de. You can look them up yourself with the free MX lookup tool.
- Why did a posteo.de 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; Posteo gave a clear rejection for a missing mailbox when we tested it.
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