Summary
- Registrar
- —
- Status
- Created on
- April 1, 1996
- Expires on
- December 31, 2028
- Name servers
- ns3.corpnet.pl, ns4.corpnet.pl, ns1.corpnet.pl, ns2.corpnet.pl
- Mail servers
- mailin.tpsa.pl, mailinz.tpsa.pl
- SPF
- Strict
- DKIM
- No key found among the common selectors
- Website
- See the website
Authorized senders (SPF)
E-mails sent by any other server are rejected.
SPF lists the servers allowed to send e-mails for centertel.pl.
| Rule | Value | Result |
|---|---|---|
| ip4 | 194.9.223.0/24 | Allowed |
| mx | — | Allowed |
| a | mta-out1.centertel.pl | Allowed |
| ip4 | 217.97.216.4/32 | Allowed |
| ip4 | 212.160.172.10/32 | Allowed |
| ip4 | 193.110.121.235 | Allowed |
| ip4 | 193.110.121.236 | Allowed |
| ip4 | 80.48.209.10 | Allowed |
| all | — | Rejected |
Top-level DNS lookups: 2 of 10 allowed
Record
v=spf1 ip4:194.9.223.0/24 mx a:mta-out1.centertel.pl ip4:217.97.216.4/32 ip4:212.160.172.10/32 ip4:193.110.121.235 ip4:193.110.121.236 ip4:80.48.209.10 -all
MX, SPF, DKIM and DMARC: the e-mail records
Four DNS records make a domain's e-mail work. MX says where e-mails sent to centertel.pl arrive; SPF, DKIM and DMARC let mail servers check that an e-mail claiming to come from centertel.pl was really sent by this domain, which protects it against spoofing.
MX
An MX (Mail Exchanger) record designates a server that receives e-mails sent to the domain. When someone writes to an @centertel.pl address, their mail server queries the DNS for the domain's MX records, then delivers the message to the server they point to.
Example record
centertel.pl MX 10 mx1.centertel.pl. centertel.pl MX 20 mx2.centertel.pl.
What the record contains
- 10, 20
- Priority: the server with the lowest number is tried first. Servers with equal priority share the load.
- mx1.centertel.pl.
- Host name of the mail server. It must point to an A or AAAA record: an IP address or an alias (CNAME) is not allowed here.
- 0 .
- An MX "0 .", called a null MX, declares that the domain accepts no e-mail: sending servers give up at once instead of retrying.
Declaring at least two servers with different priorities avoids losing e-mails during an outage: sending servers retry for several days and fall back on the backup server. Without any MX, they try to deliver directly to the IP address of the domain.
SPF
SPF (Sender Policy Framework) is a TXT record listing the servers allowed to send e-mails on behalf of the domain. The receiving server checks that the sender is on this list. The final "all" rule says what to do with other servers: reject them (-all), flag their e-mails as suspicious (~all) or make no decision (?all).
Example record
centertel.pl TXT "v=spf1 mx include:_spf.google.com ip4:192.0.2.10 -all"
What the record contains
- v=spf1
- Identifies the record as an SPF policy. It must come first.
- ip4, ip6
- Allows a specific IP address or an address range, for example ip4:192.0.2.0/24.
- a, mx
- Allows the addresses of the domain itself (A record) or those of its mail servers (MX).
- include
- Allows the servers of another domain, usually a sending service: include:_spf.google.com for Google Workspace.
- -all, ~all
- Final rule, applied to every other server. Its qualifier decides what happens to them: - rejects them, ~ flags their e-mails as suspicious, ? makes no decision, + accepts them (avoid it).
A domain must publish only one SPF record, and its evaluation cannot exceed 10 DNS lookups (include, a, mx, exists, redirect). Beyond that, mail servers treat it as invalid.
DKIM
DKIM (DomainKeys Identified Mail) signs every outgoing e-mail with a private key. The matching public key is published in a TXT record at selector._domainkey.centertel.pl, so the recipient can check that the message really comes from the domain and was not altered on the way. The selector is chosen by each sending service and cannot be guessed: Dataweaz checks the most common ones (Google Workspace, Microsoft 365, Mailchimp, SendGrid…), so a key published under another selector may exist without appearing here.
Example record
google._domainkey.centertel.pl TXT "v=DKIM1; k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA…"
What the record contains
- v=DKIM1
- Protocol version. Optional but recommended, in which case it must come first.
- k
- Key algorithm: rsa, the most common, or ed25519.
- p
- Public key, base64-encoded. An empty value means the key has been revoked.
- t
- Flags: y marks a key in testing, whose failures must not be penalized; s forbids its use for subdomains.
Each sending service publishes its key under its own selector (google, selector1, k1…), which allows several keys and seamless rotation. A 2048-bit RSA key is recommended today.
DMARC
DMARC (Domain-based Message Authentication, Reporting and Conformance) builds on SPF and DKIM. Published on _dmarc.centertel.pl, it tells mail servers what to do with an e-mail that fails these checks (let it through, send it to spam or reject it) and where to send reports.
Example record
_dmarc.centertel.pl TXT "v=DMARC1; p=quarantine; rua=mailto:[email protected]; adkim=r; aspf=r"
What the record contains
- v=DMARC1
- Identifies the record as a DMARC policy. It must come first.
- p
- Policy applied to e-mails that fail the checks: none (monitoring only), quarantine (spam folder) or reject.
- sp
- Subdomain policy. Without it, subdomains follow the domain's policy.
- rua
- Address that receives daily aggregate reports about e-mails sent on behalf of the domain, whether they pass the checks or not.
- ruf
- Address that receives detailed failure reports, message by message. Few providers still send them.
- pct
- Percentage of e-mails subject to the policy, for a gradual rollout. 100 by default.
- adkim, aspf
- DKIM and SPF alignment: r (relaxed, a subdomain of the same domain is enough) or s (strict, the domain must be identical).
To roll out DMARC without blocking legitimate e-mails, start with p=none and an rua address, analyze the reports to find every service sending on behalf of the domain, then move to quarantine and finally to reject.
DNS records of centertel.pl
IP addresses (A and AAAA)
An A record maps the domain name to an IPv4 address: the address of the server that browsers contact to display the website. The AAAA record does the same for an IPv6 address. A domain can have several of them to spread visits across several servers.
| Type | IP address |
|---|---|
| A | 80.48.169.1 |
Name servers (NS)
NS records designate the authoritative DNS servers of the domain: they answer every question about its other records (A, MX, TXT…). They are provided by the registrar, the hosting provider or a dedicated DNS service, and several servers are declared so that the domain keeps working if one of them fails.
| Server | IP address |
|---|---|
| ns3.corpnet.pl | 80.50.50.200 |
| ns4.corpnet.pl | 80.50.50.180 |
| ns1.corpnet.pl | 80.50.50.100 |
| ns2.corpnet.pl | 80.50.50.150 |
Mail servers (MX)
MX records point to the servers that receive e-mails sent to the domain, that is to @centertel.pl addresses. Each server has a priority: the one with the lowest number is tried first, the others take over if it fails. Without an MX record, the domain cannot receive e-mails.
| Priority | Server | IP address |
|---|---|---|
| 20 | mailin.tpsa.pl | 212.160.172.68 |
| 30 | mailinz.tpsa.pl | 80.48.209.10 |
TXT records
TXT records hold free text. They are used to prove ownership of the domain to online services (Google, Microsoft, Facebook…) and to publish e-mail security rules: SPF on the domain itself, DMARC on _dmarc.centertel.pl.
| Name | Content |
|---|---|
| centertel.pl | v=spf1 ip4:194.9.223.0/24 mx a:mta-out1.centertel.pl ip4:217.97.216.4/32 ip4:212.160.172.10/32 ip4:193.110.121.235 ip4:193.110.121.236 ip4:80.48.209.10 -all |
| centertel.pl | _om5wviti6bl011eif4pjnz382mzop12 |
| centertel.pl | vM8vhgRdjcj8ysMLzd5IN2LXrExMX28HZS92uxj9CgKttjyvY9KXks0ewI9CAkesnuT7O2l1O55RDoS9j/FnHQ== |
| centertel.pl | _ykzgth0wes12vr6x80i1xyibach5w13 |
| centertel.pl | mojecertpl-site-verification-e0XtWUbrLE6LHa2jP6C0hrEVJdcethCJ |
| centertel.pl | MS=ms38104253 |
| centertel.pl | _l8b804q8290v8wyp46s2b52f4rpsdsz |
| centertel.pl | 348fa4c92022e5c6a032b7b0d67c337fbc9155a06910b5643de5dc380bfda7fb |
Related IP addresses
IPv4 addresses used by centertel.pl: website, name servers, mail servers and senders authorized by SPF.
| IP address | Used for | /24 block |
|---|---|---|
| 80.48.169.1 | Website | 80.48.169.0/24 |
| 80.50.50.200 | Name server ns3.corpnet.pl | 80.50.50.0/24 |
| 80.50.50.180 | Name server ns4.corpnet.pl | 80.50.50.0/24 |
| 80.50.50.100 | Name server ns1.corpnet.pl | 80.50.50.0/24 |
| 80.50.50.150 | Name server ns2.corpnet.pl | 80.50.50.0/24 |
| 212.160.172.68 | Mail server mailin.tpsa.pl | 212.160.172.0/24 |
| 80.48.209.10 | Mail server mailinz.tpsa.pl, Authorized by SPF | 80.48.209.0/24 |
| 217.97.216.4 | Authorized by SPF | 217.97.216.0/24 |
| 212.160.172.10 | Authorized by SPF | 212.160.172.0/24 |
| 193.110.121.235 | Authorized by SPF | 193.110.121.0/24 |
| 193.110.121.236 | Authorized by SPF | 193.110.121.0/24 |
WHOIS of the domain centertel.pl
DOMAIN NAME: centertel.pl
registrant type: organization
nameservers: ns1.corpnet.pl. [80.50.50.100][2a01:1700:2:1::3264]
ns2.corpnet.pl. [80.50.50.150][2a01:1700:3:2::3296]
ns3.corpnet.pl. [80.50.50.200][2a01:1700:2:3::32c8]
ns4.corpnet.pl. [80.50.50.180][2a01:1700:3:4::32b4]
created: 1996.04.01 13:00:00
last modified: 2023.10.09 09:19:49
renewal date: 2028.12.31 13:00:00
option: no
dnssec: Unsigned
REGISTRAR:
AZ.pl Sp. z o.o.
ul. Zbożowa 4
70-653 Szczecin
Polska/Poland
Tel: +48.914243780
https://az.pl/
[email protected]
WHOIS database responses: https://dns.pl/en/whois
WHOIS displays data with a delay not exceeding 15 minutes in relation to the .pl Registry system
% Query time: 441 msec
% WHEN: Thu Oct 01 18:43:47 UTC 2026