What does MXIN501 mean in a Ziggo bounce?

It is Ziggo's own code. The 550 and the words "mailbox unknown" in the same reply carry the verdict: the mailbox doesn't exist, so treat it as a hard bounce.

Can I keep my Ziggo address after I cancel?

Ziggo's help page says no: you can't keep a Ziggo address after cancelling or switching provider, and access to the mail continues for six months after cancellation.

Is there a free bulk Ziggo checker?

Yes. This page checks a whole list for syntax, duplicates, typo domains and dead domains for free, asks Ziggo's server about 10 mailboxes live, and gives 100 free email checks with a Google sign-in. No card.

Will the Ziggo 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 Ziggo?

They are checked as normal addresses and marked as another provider. The live check asks about the Ziggo rows first.

Bulk Ziggo email checker: check a list of ziggo.nl addresses at once

In short: Checks many ziggo.nl addresses at once: duplicates and +tag repeats flagged, and 10 mailboxes asked live at Ziggo's server. Limit: Ziggo doesn't publish how its servers answer mailbox checks; the handling here is from our own checks, which can change.

A bulk Ziggo email checker tests many ziggo.nl addresses at once. Syntax, duplicates and dead domains are flagged in your browser, then the first 10 are asked live at Ziggo's mail server, which rejected made-up addresses with 550 MXIN501 mailbox … 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 ziggo.nl rows? Upload the whole list: every Ziggo row gets the same live mailbox check.

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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 now See pricing

ziggo.nl addresses, one per line

Upload a CSV or TXT fileRuns in your browser. Only the domains are sent, to look up their mail servers; addresses stay on your device.

By SimpleVerifier Team · Last updated November 12, 2026

How do I check a whole list of Ziggo addresses?

Export the list as a CSV or copy the email column; Ziggo 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.

Check which of these mailboxes really exist

How do I check if many Ziggo 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 Ziggo 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 Ziggo'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.jansen@ziggo.nl, jan.jansen+nieuws@ziggo.nl, Jan.Jansen@ziggo.nl, another ziggo.nl, a kpnmail.nl and a company address.
You get: Jan.Jansen@ziggo.nl is marked as a duplicate of row 1 and comes off; jan.jansen+nieuws@ziggo.nl is marked as row 1 plus a +tag and kept; the kpnmail.nl and company rows are marked as another provider. The live check asks Ziggo about the Ziggo 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 Ziggo addresses exist in bulk?

Yes. On 8 November 2026 ziggo.nl published two MX hosts, mxin5.ziggo.nl and mxin10.ziggo.nl. On 12 October 2026 they answered a made-up address at RCPT TO with 550 MXIN501 mailbox … unknown, and a fresh one got the same rejection on 8 November, so a Ziggo row's result comes from Ziggo's own server.

MXIN501 is Ziggo's own code; the 550 and the words "mailbox unknown" carry the verdict. Only ziggo.nl counts as a Ziggo row, so kpnmail.nl and the older upcmail.nl or home.nl domains are checked as normal addresses and marked as another provider.

Why do ziggo.nl addresses go dead?

Ziggo's mail help page says you can't keep a Ziggo address after cancelling or switching provider; access to the mail continues for six months after cancellation.

So a ziggo.nl address on an old list often belongs to someone who switched providers. Re-check Dutch lists before a campaign and remove the rows that come back invalid.

What does the bulk Ziggo 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 ziggo.nl 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, Ziggo 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 Ziggo checker.

What does each check catch on a Ziggo 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: Ziggo answers at RCPT TO (550 MXIN501 mailbox 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 ziggo.nl on 12 October and 8 November 2026.

Who uses this tool, and for what?

Dutch shops and newsletters: Drop ziggo.nl rows whose owner switched provider before the next campaign.
Lead buyers: Check the Dutch provider 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?

Ziggo doesn't publish how its servers answer mailbox checks; the handling here is from our own checks, which can change.
Only ziggo.nl is matched; the older upcmail.nl, home.nl and similar Ziggo-era domains are checked as normal addresses.
A +tag repeat is marked as possibly the same inbox, not merged, because this page doesn't verify how Ziggo 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

What does MXIN501 mean in a Ziggo bounce?: It is Ziggo's own code. The 550 and the words "mailbox unknown" in the same reply carry the verdict: the mailbox doesn't exist, so treat it as a hard bounce.
Can I keep my Ziggo address after I cancel?: Ziggo's help page says no: you can't keep a Ziggo address after cancelling or switching provider, and access to the mail continues for six months after cancellation.
Is there a free bulk Ziggo checker?: Yes. This page checks a whole list for syntax, duplicates, typo domains and dead domains for free, asks Ziggo's server about 10 mailboxes live, and gives 100 free email checks with a Google sign-in. No card.
Will the Ziggo 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 Ziggo?: They are checked as normal addresses and marked as another provider. The live check asks about the Ziggo 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

Get started — $39/mo See the published limits first

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.