Optimum Email works in any mail app that speaks IMAP. Incoming mail (IMAP): mail.optimum.net, port 993 (SSL/TLS). Outgoing mail (SMTP): mail.optimum.net, port 465 (SSL/TLS). The user name is your full email address, and the password is the password of that email address. In LocalInbox, choose Other IMAP account and type these in under Server settings.
Optimum stopped creating new email accounts in May 2021. Existing ones still work in mail apps.
Server settings
| Server | Host name | Port | Security |
|---|---|---|---|
| Incoming (IMAP) | mail.optimum.net | 993 | SSL/TLS |
| Outgoing (SMTP) | mail.optimum.net | 465 | SSL/TLS |
| Incoming (POP3) | mail.optimum.net | 995 | SSL/TLS |
For optimum.net and optonline.net addresses. Suddenlink addresses use imap.suddenlink.net, smtp.suddenlink.net and pop.suddenlink.net, on the same ports.
What the ports and security mean: IMAP ports and SMTP ports.
POP3 is for apps that use it. LocalInbox uses IMAP, so read, moved and deleted mail stays the same on every device: POP3 and IMAP compared.
Steps
- In LocalInbox, open Settings › Accounts and click Add Account (or use the welcome screen the first time).
- Choose Other IMAP account. Enter your Optimum address, and the password of that email address as the password.
- Open Server settings. Under Incoming mail (IMAP), enter mail.optimum.net and port 993, and choose TLS.
- Under Outgoing mail (SMTP), enter mail.optimum.net and port 465, and choose TLS.
- Leave User name empty, and LocalInbox signs in with your full address, which is what Optimum expects.
- Click Connect. LocalInbox signs in and starts syncing your mail.
Troubleshooting
Optimum turns down my address as the user name
Optimum's help for home customers says to use the full address, but its business help page says the part before @optimum.net or @optonline.net. Try that under Server settings › User name.
LocalInbox says the password is wrong
LocalInbox needs the password of that email address. Copy it again, without spaces before or after.
LocalInbox says it can't connect
The message says what to fix: nothing answering at the port, the wrong kind of TLS for the port, an untrusted certificate, an unknown server name, or a timeout. Check what you typed under Server settings against the table at the top of this page.
Sources
Optimum Email's settings were checked against its own help pages in November 2026 and can change. The steps in LocalInbox come from the app.
Questions
What are the Optimum Email IMAP and SMTP settings?
Incoming (IMAP): mail.optimum.net, port 993, SSL/TLS. Outgoing (SMTP): mail.optimum.net, port 465, SSL/TLS. For optimum.net and optonline.net addresses. Suddenlink addresses use imap.suddenlink.net, smtp.suddenlink.net and pop.suddenlink.net, on the same ports.
Where does LocalInbox keep the password?
In the macOS Keychain on your Mac. It's never written to a file or sent anywhere except your mail server.
What are the Optimum Email POP3 settings?
Incoming (POP3): mail.optimum.net, port 995, SSL/TLS, for apps that use POP3; outgoing mail goes through the same SMTP server as with IMAP. LocalInbox uses IMAP instead, which keeps read, moved and deleted mail the same in webmail, on your phone and on your Mac. POP3 downloads mail to one device.
Can I add Optimum Email on iPhone or iPad?
Yes, the same way, in LocalInbox for iPhone and iPad: Settings › Accounts › Add Account, then Other IMAP account. Type in the same server settings and password. Already added it on your Mac? Add Account › From your Mac copies it with a QR code, password included. https://localinbox.app/iphone