Bulk Optimum email checker: check a list of optonline.net addresses at once
In short: Checks many optonline.net and optimum.net addresses at once: duplicates and +tag repeats flagged, and 10 mailboxes asked live at Optimum's server. Limit: Optimum doesn't publish how its servers answer mailbox checks; the handling here is from our own checks, which can change.
A bulk Optimum email checker tests many optonline.net and optimum.net addresses at once. Syntax, duplicates and dead domains are flagged in your browser, then the first 10 are asked live at Optimum's mail server, which rejected made-up optonline.net addresses with 550 … User unknown on 13 October and 8 November 2026. A missing mailbox comes back invalid, a real one valid, an unclear answer risky.
More than 10 optonline.net rows? Upload the whole list: every Optimum 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 Optimum addresses?
- Export the list as a CSV or copy the email column; Optimum 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 Optimum 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 Optimum 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 Optimum'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:
jane.doe@optonline.net,jane.doe+deals@optonline.net,Jane.Doe@optonline.net, another optonline.net, an optimum.net and a company address. - You get
Jane.Doe@optonline.netis marked as a duplicate of row 1 and comes off;jane.doe+deals@optonline.netis marked as row 1 plus a +tag and kept; the company address is marked as another provider. The live check asks Optimum about the Optimum rows first, and a missing mailbox comes back invalid.- 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 optonline.net addresses exist in bulk?
Yes. On 8 November 2026 optonline.net and optimum.net both published one MX host, mx.altice.prod.cloud.openwave.ai, an Openwave-hosted server rather than a host under optonline.net. On 13 October 2026 it answered a made-up optonline.net address at RCPT TO with 550 RCPT TO:<…@optonline.net> User unknown, and a fresh one got the same rejection on 8 November.
So an Optimum row's result comes from Optimum's own server: a rejection is invalid, an acceptance valid, and anything unclear risky.
Why do Optimum addresses disappear?
Optimum's email FAQ says an inbox and all its content are deleted after 90 days of email account inactivity, and every address on an account is deleted within 90 days of the Internet service being disconnected.
The same FAQ says Optimum stopped letting customers create new Optimum email accounts on 4 May 2021, so the pool of optonline.net addresses only shrinks. Re-check optonline.net rows older than about three months before you send.
What does the bulk Optimum 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 optonline.net and optimum.net 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, Optimum 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 Optimum checker.
What does each check catch on a Optimum 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: Optimum answers at RCPT TO (550 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 optonline.net on 13 October and 8 November 2026.
Who uses this tool, and for what?
- Local businesses in the New York area
- Drop optonline.net addresses deleted after 90 idle days before a campaign.
- Anyone cleaning an old US list
- Separate Optimum mailboxes the server rejected from ones it accepted.
- List owners
- Find repeated rows and +tag copies before counting your audience.
What can’t this tool tell you?
- Optimum doesn't publish how its servers answer mailbox checks; the handling here is from our own checks, which can change.
- A valid result shows the server accepted the mailbox today, not that the account has been used within 90 days.
- A +tag repeat is marked as possibly the same inbox, not merged, because this page doesn't verify how Optimum 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
- Does Optimum delete inactive email accounts?
- Optimum's FAQ says an inbox and all its content are deleted after 90 days of email account inactivity, and every address on an account within 90 days of an Internet disconnection.
- Can people still get a new optonline.net address?
- No. Optimum's FAQ says that since 4 May 2021 it no longer lets new or existing Internet customers create new Optimum email accounts, so every optonline.net address on your list is at least that old.
- Is there a free bulk Optimum checker?
- Yes. This page checks a whole list for syntax, duplicates, typo domains and dead domains for free, asks Optimum's server about 10 mailboxes live, and gives 100 free email checks with a Google sign-in. No card.
- Will the Optimum 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 Optimum?
- They are checked as normal addresses and marked as another provider. The live check asks about the Optimum 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.