Bulk Onet email checker: check a list of onet.pl addresses at once
In short: Checks many onet.pl addresses at once: duplicates and +tag repeats flagged, and 10 mailboxes asked live at Onet Poczta's server. Limit: Onet doesn't publish how its servers answer mailbox checks; the handling here is from our own checks, which can change.
A bulk Onet email checker tests many onet.pl addresses at once. Syntax, duplicates and dead domains are flagged in your browser, then the first 10 are asked live at Onet Poczta's mail server, which rejected made-up addresses with 550 5.1.1 … User unknown on 12 October and 8 November 2026. A missing mailbox comes back invalid, a real one valid, an unclear answer risky.
More than 10 onet.pl rows? Upload the whole list: every Onet row gets the same live mailbox check.
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. Check your list free nowSee pricing
By SimpleVerifier Team · Last updated
How do I check a whole list of Onet addresses?
- Export the list as a CSV or copy the email column; Onet rows and every other domain can go in together.
- Upload or paste it at /verify. Every address gets a live mailbox check, and the first 100 email checks are free with a Google sign-in, no card.
How do I check if many onet.pl addresses exist?
- Paste the addresses, one per line, or a CSV column of them. Addresses at other providers are checked as normal addresses and marked.
- Press Check the Onet addresses.
- Read the flagged rows: a typo domain, a duplicate, a +tag repeat of an earlier row, or a domain with no mail server.
- Download the clean list. Notes stay on it; only rows that fail a check come off.
- The first 10 go to Onet's mail server for a live answer. Sign in with Google to check the rest with 100 free email checks.
Example
- You enter
- 6 addresses:
jan.kowalski@onet.pl,jan.kowalski+promo@onet.pl,Jan.Kowalski@onet.pl, another onet.pl, a wp.pl and a company address. - You get
Jan.Kowalski@onet.plis marked as a duplicate of row 1 and comes off;jan.kowalski+promo@onet.plis marked as row 1 plus a +tag and kept; the wp.pl and company rows are marked as another provider. The live check asks Onet about the Onet rows first.- Limits
- The browser pass covers the first 5,000 rows; only domains leave your device. 10 live checks a day without an account, then the free checks with a Google sign-in.
Can you check if onet.pl addresses exist in bulk?
Yes. On 8 November 2026 onet.pl published one MX host, mx.poczta.onet.pl. On 12 October 2026 it answered a made-up address at RCPT TO with 550 5.1.1 Recipient address rejected: User unknown, and a fresh one got the same rejection on 8 November, so an Onet row's result comes from Onet's own server.
Only onet.pl counts as an Onet row. wp.pl and o2.pl rows on the same list are checked as normal addresses and marked as another provider.
Why do onet.pl addresses go dead?
Onet's Poczta terms let it end the free service and delete an account with everything in it after at least 12 months without a login. The same terms say a deleted address can later go to another user, but not before at least 12 months after deletion, and some addresses may never be released.
Onet's advice for bulk senders asks for SPF, DKIM, DMARC and BIMI, a List-Unsubscribe header and double opt-in. A Polish list that is a year or two old deserves a re-check before a campaign.
What does the bulk Onet check do to my list?
The pass over the whole list runs in your browser: syntax, duplicates, typo domains and role addresses. Only the unique domains are sent out, to look up mail servers and the disposable list. Rows at onet.pl are matched by the part after the @, so an address at any other domain is checked as a normal address and marked as another provider.
Then the first 10 addresses, Onet rows first, are asked live at the mail server without sending anything. Sign in with Google to check the rest with 100 free email checks. For one address with full notes, use the Onet checker.
What does each check catch on a Onet list?
| Check | Can we confirm it? | Result when it fails |
|---|---|---|
| Syntax and duplicates | Yes, in your browser | Bad syntax comes off; a duplicate is marked |
| Domain and mail server (MX) | Yes, from DNS | No mail server comes off |
| Disposable or role address | Yes | Disposable comes off; a role address is marked |
| The mailbox exists | Yes: Onet answers at RCPT TO (550 5.1.1 User unknown) | Invalid, "Mailbox not found"; an unclear reply is risky |
| Someone reads the inbox | No checker can | Use opens, replies or a small first send |
Mailbox behaviour as measured on onet.pl on 12 October and 8 November 2026.
Who uses this tool, and for what?
- Polish shops and newsletters
- Drop onet.pl rows whose account was deleted after a year without a login before the next campaign.
- Lead buyers
- Check the Polish webmail rows of a bought list before importing it.
- List owners
- Find repeated rows and +tag copies before counting your audience.
What can’t this tool tell you?
- Onet doesn't publish how its servers answer mailbox checks; the handling here is from our own checks, which can change.
- Typo-domain detection covers the big webmail domains and slips like .con, not Polish domain misspellings.
- A +tag repeat is marked as possibly the same inbox, not merged, because this page doesn't verify how Onet treats tags.
- The live check covers 10 addresses without an account; risky results there can mean the check was cut short, so try again later.
- Valid means the mailbox exists today, not that anyone reads it.
Common questions
- Can an old onet.pl address belong to someone new?
- Onet's terms say a deleted address can later go to another user, but not before at least 12 months after deletion. A valid result shows the mailbox exists today, not that it is the same person.
- Are wp.pl and o2.pl Onet addresses?
- No. Only onet.pl counts as an Onet row here; wp.pl and o2.pl rows are checked as normal addresses and marked as another provider.
- Is there a free bulk Onet checker?
- Yes. This page checks a whole list for syntax, duplicates, typo domains and dead domains for free, asks Onet's server about 10 mailboxes live, and gives 100 free email checks with a Google sign-in. No card.
- Will the Onet users know I checked their address?
- No. The check ends after the mail server answers about the mailbox, before any message content is sent, so nothing arrives in their inbox.
- What happens to the addresses on my list that aren't Onet?
- They are checked as normal addresses and marked as another provider. The live check asks about the Onet rows first.
Sources
A tidy list can still be full of dead addresses.
Extracting, deduplicating and syntax checks all work on the text of an address. None of them can tell whether the mailbox exists. Only the server that hosts it can answer that, through an SMTP check, and that is what the paid product does.
- Upload the cleaned file as it is: CSVs up to 100,000 rows
- A real SMTP mailbox check on every row, with catch-all detection
- Small list? Starter at $9/mo covers 2,500 emails a month, cancel anytime
Plans from $9 a month, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.