Reading time: 9 min · Last verified: August 2026 · SMTPedia editorial team
Optimum publishes exactly one mail hostname and six ports, and it tells you plainly which three of those ports it wants you to use. The problem is that almost nothing else agrees with it. Search for the settings and the first thing on the page is an AI summary that leads with port 587, which is the port Optimum itself labels “Not recommended. Legacy mail clients only”. Follow it and you will be configuring the row the provider deprecated, on a connection type it does not describe.
The server is mail.optimum.net for incoming and outgoing alike. Use 993 for IMAP, 995 for POP3 and 465 for SMTP, all with SSL, and tick the box that says the outgoing server requires authentication. Optimum publishes 143, 110 and 587 as well, and it marks all three with the same warning: not recommended, legacy mail clients only. The Google AI Overview currently prints the outgoing port as “587 (or 465)”, which reverses the provider’s own order of preference.
The Settings Optimum Actually Publishes
Every value below comes from the Optimum email server settings article in the Optimum FAQ, which is the provider’s own reference page for third party mail clients. Nothing here is reconstructed from a forum thread or a client vendor’s setup page, and the distinction matters more on this provider than on most, for reasons the next section covers.
| Protocol | Server | Port | Encryption |
|---|---|---|---|
| IMAP (incoming) | mail.optimum.net | 993 | SSL, recommended |
| POP3 (incoming) | mail.optimum.net | 995 | SSL, recommended |
| SMTP (outgoing) | mail.optimum.net | 465 | SSL, recommended |
| IMAP (legacy) | mail.optimum.net | 143 | Not recommended |
| POP3 (legacy) | mail.optimum.net | 110 | Not recommended |
| SMTP (legacy) | mail.optimum.net | 587 | Not recommended |
One hostname, six ports, one recommendation per protocol. Optimum does not publish a separate incoming and outgoing name, and it does not publish an imap., pop. or smtp. prefixed host for the optimum.net domain. Outgoing authentication is required in every configuration: the setting appears in the FAQ as the checkbox labelled “My SMTP server requires authentication”. | |||
The three legacy rows are not a fallback menu. Optimum attaches the identical phrase to each of them, “Not recommended. Legacy mail clients only”, and no modern client needs any of the three. If you are on 143 or 110 today, the mailbox is reachable in cleartext, which is worth changing for its own sake rather than because anything has broken yet. The wider case for the encrypted ports is in the reference on SSL and TLS for email, certificates and MTA-STS, and the protocol level differences between the two incoming options are laid out in the reference on email protocols and their ports.
Port 587 Is the Deprecated Row, Not the Modern One
This is where Optimum breaks the pattern, and where following general advice will steer you wrong.
Across the industry, port 587 with STARTTLS is the submission port, and 465 spent years being described as the deprecated one. That history is real and it is why so many setup guides reach for 587 by reflex. On Optimum the labels are the other way round: 465 carries the “Secure Connection. Recommended if your mail client supports” note, and 587 carries the legacy warning. Optimum never describes 587 as a STARTTLS port, and it never pairs 587 with an encryption setting at all.
The row Optimum recommends. Implicit TLS from the first byte, no upgrade step, nothing to negotiate. Set the encryption field to SSL or SSL/TLS, never to STARTTLS, and never to None.
Optimum lists it for old clients that cannot do implicit TLS. Because the provider publishes no encryption value for this row, a client that offers you a choice is guessing. If it connects, verify what it negotiated rather than assuming.
The combination the AI summary invites by printing “587 (or 465)” next to “STARTTLS, TLS, or SSL/TLS” as though the three were interchangeable. A client that opens 465 expecting to issue STARTTLS fails during the handshake, which is a different failure from a rejected password.
The failure modes are worth telling apart because their error text is misleading. An encryption mismatch typically surfaces as a connection or certificate error rather than a credential error, and the family of responses is documented in the entry on the 550 Must Issue STARTTLS response and what triggers it. A missing authentication tick produces something quite different, usually in the shape described in the 454 4.7.1 relay access denied reference. If your client reports a numeric code you do not recognise, the complete SMTP response code directory will name it.
Optimum Contradicts Itself on the Username
The single most common reason an Optimum mailbox refuses to authenticate is the username field, and Optimum is the reason for the confusion. Two of its own support pages answer the question differently.
| Optimum page | What it says the username is |
|---|---|
| Email server settings article | “Your Optimum ID, the portion to the left of @optimum.net or @optonline.net” |
| Fixing common email issues article | “Your full email address, including the @domain.net at the end” |
These are not two ways of saying the same thing. One is jsmith and the other is jsmith@optimum.net. The settings page strips the domain; the troubleshooting page insists on it and gives @optimum.net and @suddenlink.net as examples. Third party guidance splits the same way, and the AI Overview hedges by giving the short form and then adding that some apps may require the full address.
Practical order: try the full email address first. It is the form the troubleshooting page gives, it is the form most clients prefill, and it is unambiguous when an account has addresses on more than one of the three domains. If authentication fails on the full address and the password is definitely correct, retry with the portion to the left of the at sign before you reset anything. Two attempts settle it, and neither costs you a password reset you did not need.
One thing Optimum does not publish anywhere: an application specific password, an app password, or any OAuth flow for third party clients. Your normal mailbox password is the credential. That is a meaningful difference from several neighbouring providers, and it is why the setup does not resemble the AT&T configuration and its mandatory secure mail key, which cannot be completed with an account password at all.
Three Address Domains, One Mail System
Optimum addresses come in three shapes: @optimum.net, the legacy Optimum Online @optonline.net, and @suddenlink.net from the Suddenlink brand that Altice folded into Optimum. Neither Optimum support page lists all three together, which leaves Suddenlink customers in particular unsure whether the published settings apply to them.
The DNS answers this cleanly. On 28 August 2026, resolved from an outside resolver and confirmed against a second one, all three domains publish a single identical MX record:
| Address domain | MX record |
|---|---|
| optimum.net | mx.altice.prod.cloud.openwave.ai |
| optonline.net | mx.altice.prod.cloud.openwave.ai |
| suddenlink.net | mx.altice.prod.cloud.openwave.ai |
One record, one preference value, no per brand variation. The hostname names an Altice production tenancy hosted on Openwave cloud infrastructure, which is what the DNS states rather than something Optimum documents in its FAQ. Inbound mail for all three domains lands in the same place, and the address suffix is a label rather than a routing decision. Optimum reflects this on the account side too: its sign in guidance tells customers with either an Optimum or a Suddenlink address to check mail at optimum.net.
This is the same shape of finding as the Cox configuration, where cox.net addresses are served by Yahoo infrastructure, and it explains why the settings table has one hostname rather than three. If you are unsure how to read a domain’s mail routing yourself, the method is in the guide to configuring and troubleshooting MX records.
Hostnames that resolve are not hostnames Optimum supports
Resolution was checked on the same date with deliberate negative controls, because a name that answers the DNS proves only that a record exists.
| Hostname | Resolution | What it means |
|---|---|---|
| mail.optimum.net | Rotating set in 66.179.105.0/24 | The documented host |
| mail.optonline.net | The same rotating set | Not an alternative, the same service |
| imap.optimum.net, pop.optimum.net, smtp.optimum.net | No record | Guessed names, never documented |
| mail.suddenlink.net | No record | Suddenlink users take the Optimum host |
| Random subdomain on all three domains | No record | Negative control: no wildcard in play |
Two results are worth keeping. First, mail.optonline.net and mail.optimum.net return the identical address pool, so the AI Overview phrasing “mail.optimum.net (or mail.optonline.net)” describes one host under two names rather than a choice between two servers. Whichever you already have configured is fine, and switching between them changes nothing. Second, the conventional per protocol prefixes do not exist here at all. That convention is common enough elsewhere that clients suggest it, and the differences between provider naming schemes are collected in the protocol and port reference.
Setting It Up in a Mail Client
The values are identical on every platform. A page promising special Optimum settings for iPhone is describing an interface, not a protocol. What changes between clients is only how much guessing they do before you get to type anything.
Choose manual setup and IMAP rather than letting autodiscover run. Then open the outgoing server tab and tick that the SMTP server requires authentication, using the same credentials as incoming. Outlook does not set that box for you, and the account will receive mail perfectly while refusing to send. Reference: the Microsoft Outlook client entry.
Add the account as Other, not by picking a named provider, so Mail does not substitute its own guesses. Fill the outgoing password field even where iOS marks it optional; left blank, sending fails later with no obvious cause. Reference: the Apple Mail client entry.
Use Manual setup and choose IMAP or POP, never Exchange. Note that Optimum’s own Android walkthrough instructs users to select SSL with the “accept all certificates” option; that weakens validation, so prefer plain SSL first and only fall back if the client genuinely refuses to connect.
If you are choosing between the two incoming protocols rather than copying an existing setup, IMAP is the right default on any account read from more than one device, and the trade-offs are set out in the IMAP configuration guide covering ports and folder mapping and in the POP3 guide covering server retention. For the outgoing side generally, independent of provider, there is the SMTP setup guide for authentication and TLS in any client.
When Sending Or Receiving Stops
Work in this order. Each step rules something out rather than changing a setting hopefully.
- Sign in to webmail at optimum.net. If webmail accepts the password, the account and the password are fine and the fault is in the client. If webmail refuses it, nothing you change in the client will help.
- Check the outgoing authentication box. Receiving works and sending does not is the signature of this one setting, on every client, more often than any other cause.
- Check the encryption label against the port. 465 pairs with SSL or SSL/TLS. If the client is set to STARTTLS or None on 465, correct it before touching credentials.
- Try the other username form. Full address first, then the portion to the left of the at sign, for the reason set out above.
- Check mail forwarding and filters in webmail. Optimum’s own troubleshooting page points here for missing incoming mail: a forward or a filter set up long ago is a common cause of mail that appears to vanish. The wider mechanics are in the guide to email forwarding and its DMARC pitfalls.
- Read the actual error text. Mail clients bury it, but the numeric response is the fastest route to a cause, and the SMTP response code directory covers what each one means.
What Optimum Does Not Publish
These are stated as absent rather than filled in from elsewhere, because a number invented for the sake of a complete table is worse than an admitted gap.
- No published outbound sending limit. No documented messages per hour or per day figure, and no recipients per message cap. Third party roundups quote numbers for Optimum; none of them cite an Optimum page, and none is repeated here.
- No published attachment size limit and no published mailbox quota.
- No application specific password and no OAuth option for third party clients. The account password is the credential.
- No documented per protocol hostnames. One name covers incoming and outgoing.
- No encryption value stated for the 587 row, which is part of why that row should be left alone.
Where a provider does publish an outbound ceiling, it is usually the explanation for mail that stops abruptly on a configuration nobody touched. Optimum is not in that category on the public record, so an abrupt stop here points back at credentials, encryption or the forwarding rules rather than at a quota.
Frequently Asked Questions
What is the IMAP server for Optimum email?
mail.optimum.net on port 993 with SSL. Optimum publishes the same hostname for POP3 on 995 and for SMTP on 465, and it does not publish an imap.optimum.net host at all. If a client suggests one, it is guessing from a naming convention other providers use.
What are the settings for my optonline.net email account?
Identical to the optimum.net settings, on the same server. mail.optonline.net and mail.optimum.net resolve to the same address pool, and both domains publish the same single MX record, so they are one mail system under two names. Keep whichever hostname is already configured; changing it accomplishes nothing.
Is the Optimum SMTP port 465 or 587?
Optimum publishes both and recommends 465 with SSL. It lists 587 under the note “Not recommended. Legacy mail clients only”, and it does not state an encryption setting for that row. Use 465. Summaries that lead with 587 are applying a general convention that this provider does not follow.
Do Suddenlink email addresses use different servers?
No. suddenlink.net publishes the same single MX record as optimum.net and optonline.net, and mail.suddenlink.net does not resolve at all. Suddenlink addresses use mail.optimum.net with the ports above, and Optimum tells Suddenlink customers to check webmail at optimum.net.
Why am I not getting emails on my Optimum account?
Check webmail first: if the message is there, the account is receiving normally and the client is the problem, most often a POP3 setup that already downloaded and removed it. If webmail is missing it too, look at mail forwarding and mail filters in the webmail settings, which is where Optimum’s own troubleshooting article sends you. A forwarding rule set up years earlier and forgotten is a common cause.
Should my username be the full address or just the Optimum ID?
Optimum answers this two different ways on two different support pages: the settings article says the portion to the left of the at sign, the troubleshooting article says the full address including the domain. Try the full address first, then the short form. Do not reset the password until both have failed.
Are Optimum email settings different on iPhone or Android?
No. Hostname, ports and encryption are the same everywhere. On iOS, add the account as Other and fill the outgoing password even though it is marked optional. On Android, use Manual setup and pick IMAP rather than Exchange. Only the menus differ.
Settings for the other American internet providers documented on this site:
Spectrum Email Settings · Comcast Xfinity Email Settings · Verizon.net Email Settings · CenturyLink Email Settings · EarthLink Email Settings · Roadrunner Email Settings
About This Guide
These values were verified on August 28, 2026 against Optimum’s own support documentation: its email server settings article for the hostname, the six ports, the recommended and legacy labels, the outgoing authentication requirement and the Optimum ID username form; its article on fixing common email issues for the conflicting full address username form, the Suddenlink domain and the forwarding and filter checks; its sign in article for the shared webmail entry point across Optimum and Suddenlink addresses; and its Android walkthrough for the manual IMAP route. Domain routing and hostnames were resolved independently on the same date from two public resolvers, with negative controls confirming that no wildcard record is in play on optimum.net, optonline.net or suddenlink.net. The AI Overview wording quoted here was captured from a live United States desktop result on the same date. Fields Optimum does not publish, including any outbound sending limit, attachment ceiling, mailbox quota or application specific password, are recorded as absent rather than filled in from third party pages. SMTPedia re-verifies provider settings quarterly. If Optimum publishes a value that contradicts this page, the provider is right and we want to hear about it.
About the Author
Alaa · LinkedIn
Email infrastructure specialist with 8+ years of hands-on experience in SMTP, deliverability, and email verification. I’ve configured and troubleshot mail systems across Postfix, Exchange, and cloud relays, managed IP reputation and warmup campaigns, and built verification pipelines processing millions of addresses. My work spans DNS authentication (SPF, DKIM, DMARC, BIMI), bounce handling, blocklist monitoring, and compliance frameworks including CAN-SPAM and GDPR. I write every article on SMTPedia to give email professionals, developers, and marketers the accurate, RFC-grounded reference they need.
About SMTPedia
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