Mailbox provider · T-Online
How to verify a t-online.de email address
Can you verify @t-online.de addresses?
PartlyPartly. @t-online.de often refuses checking servers before the mailbox question.
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The checker does probe @t-online.de, but its server screens or defers unfamiliar checking connections. A refusal at that stage is about the connection, not the address, so it comes back risky ("Server refused our check" or "Mailbox check unavailable") and never invalid. It always checks the syntax, the domain's MX records, disposable domains and role addresses such as info@ first.
Server refused our checkMailbox check unavailableT-Online addresses usually come back inconclusive from a mailbox check. On 12 October 2026 the t-online.de mail server mx01.t-online.de refused our checking server at the greeting stage, citing the connecting server's reputation. A refusal like that says nothing about whether the address exists.
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Live DNS snapshot: t-online.de
Checked 6 November 2026, 11:14 UTCRead from DNS at the time shown and refreshed at most once a day. MX says where mail for t-online.de goes; SPF and DMARC describe mail sent from it, not whether any one address exists.
- 10
mx01.t-online.de - 10
mx02.t-online.de - 10
mx03.t-online.de - 10
mx00.t-online.de
v=spf1 ip4:194.25.134.16/28 ip4:194.25.134.80/28 ~allp=none: meets the requirement, but blocks nothing.
v=DMARC1; p=none; rua=mailto:[email protected]Look up any other domain with the MX lookup or the email provider lookup.
T-Online at a glance
| Operated by | Deutsche Telekom AGSource: T-Online postmaster page (German) |
|---|---|
| MX hosts | mx00.t-online.de, mx01.t-online.de, mx02.t-online.de, mx03.t-online.deObserved 12 October 2026 (dig MX) |
| Answer to a made-up address | Connection refused at the greeting: 554 None/bad reputation. Ask your postmaster for helpObserved 12 October 2026 (SMTP probe of a made-up recipient, no message sent) |
| Inactive accounts | When a Telekom landline ends, the address can be kept as Freemail within 180 days; after that the mailbox is deleted, locked for 90 days, then released to the publicSource: Telekom help: keep your address (German) |
| Postmaster rules | Telekom expects SMTP errors of at most 3% at peak and 1.5% on average from professional sendersSource: T-Online postmaster: bulk mail (German) |
| Postmaster rules | Bulk senders are asked to delete or block addresses they have had no contact with for more than three monthsSource: T-Online postmaster: bulk mail (German) |
What T-Online's server says about a missing mailbox
T-Online's server replied 554 None/bad reputation. Ask your postmaster for help. That refusal happened at the greeting 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 t-online.de results differ between verifiers. SMTP verification false positives explains how much to trust each answer.
The reply asks the connecting server's postmaster to contact T-Online to have the reputation reset, so the block is about the checking server rather than any address.
Telekom watches your bounce rate
Telekom's postmaster page sets a clear limit: SMTP errors should stay at or below 3% at peak and 1.5% on average, and it reads higher rates as stale addresses or missing double opt-in. It also asks bulk senders to drop addresses they have had no contact with for more than three months.
@t-online.de addresses can be reissued too. When a Telekom landline ends and the address isn't moved to Freemail within 180 days, the help page says the mailbox is deleted, the address locked for 90 days and then released to the public. An old @t-online.de contact may now belong to someone new.
Cleaning t-online.de addresses you can't check
Treat inconclusive t-online.de 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 t-online.de, send a small batch first and suppress anything that hard-bounces. If the t-online.de share of your list is small, it's often simpler to keep those rows out of a high-risk campaign than to guess.
Common questions
- Can you verify @t-online.de addresses?
- Partly. @t-online.de often refuses checking servers before the mailbox question. The checker does probe @t-online.de, but its server screens or defers unfamiliar checking connections. A refusal at that stage is about the connection, not the address, so it comes back risky ("Server refused our check" or "Mailbox check unavailable") and never invalid. It always checks the syntax, the domain's MX records, disposable domains and role addresses such as info@ first.
- Can I check if a t-online.de address exists without emailing it?
- Usually not from a checking service. On 12 October 2026 T-Online's server refused our checking connection at the greeting stage, before any mailbox question, so the result is inconclusive rather than valid or invalid.
- What mail servers does t-online.de use?
- On 12 October 2026, t-online.de published these MX hosts: mx00.t-online.de, mx01.t-online.de, mx02.t-online.de, mx03.t-online.de. You can look them up yourself with the free MX lookup tool.
- Should I delete t-online.de addresses that come back risky?
- No. For t-online.de, risky reflects how the server treats checks, not the address. Remove the ones that fail format, typo-domain and duplicate checks, then send to the rest in a small batch and suppress whatever hard-bounces.
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