Reading time: 9 min · Last verified: August 2026 · SMTPedia editorial team
Most provider settings pages fail because the web disagrees with the provider. The IONOS email settings fail for a stranger reason: IONOS disagrees with itself. Its main server reference publishes port 465 for outgoing mail and treats 587 as a fallback. Its UK glossary publishes the exact opposite, calling 587 the recommended port and 465 the alternative. A third IONOS page, the Apple Mail walkthrough, lists 587 in a column headed “SSL enabled”. All three are official. Only one of them matches what your mail client needs, and which one depends on your network rather than your account.
Start on 465 with SSL/TLS. Move to 587 with STARTTLS only if 465 will not connect. That order comes from the IONOS mail server reference itself, which lists 465 in its table and then says that if your program cannot reach the outgoing server, “access to port 465 may be blocked on your network. In this case, IONOS offers port 587.” The reverse ordering published in the IONOS UK glossary is not a different account type and not a newer policy: it is the same two ports, ranked the other way round. Both work. Neither is a fix for a wrong password.
Quick Reference: IONOS Mail Server Settings
These are the values IONOS publishes on its own mail server reference page, read in August 2026. They cover Mail Basic and Mail Business, the two mailboxes IONOS runs itself. The username is always the full email address, never the local part before the at sign, and every row is encrypted.
| Protocol | Server | Port | Encryption | Username |
|---|---|---|---|---|
| IMAP (incoming) | imap.ionos.com | 993 | SSL/TLS | Full email address |
| POP3 (incoming) | pop.ionos.com | 995 | SSL/TLS | Full email address |
| SMTP (outgoing) | smtp.ionos.com | 465 | SSL/TLS | Full email address |
| SMTP (fallback) | smtp.ionos.com | 587 | STARTTLS | Full email address |
Note the hostnames: incoming uses two different names, imap.ionos.com and pop.ionos.com. Unlike providers that answer every protocol on one endpoint, IONOS gives IMAP and POP3 separate names. Entering the IMAP hostname with the POP3 port is the single most common IONOS mail server settings error. | ||||
If those numbers are unfamiliar, the pairing is standard rather than an IONOS invention: 993 and 995 are the implicit-TLS forms of IMAP and POP3, and 465 and 587 are the two accepted ways to submit outgoing mail. The reference on email protocols and their standard ports sets out which number belongs to which service across every provider.
Port 465 or 587: What Each IONOS Page Actually Says
This is worth spelling out, because a search for the IONOS SMTP server returns all three of these pages and they do not read the same way. Here is each one, quoted rather than paraphrased.
The IONOS help article on server details for IMAP, POP3 and SMTP puts 465 with SSL/TLS in the table. Port 587 appears only afterwards, introduced by the condition that 465 “may be blocked on your network”.
The IONOS UK glossary entry for SMTP states that “the recommended SMTP port is 587 along with the TLS (or STARTTLS) security type” and that “alternatively, you can use port 465 with SSL”. The same page names port 25 as a last resort and calls it unsecured.
The IONOS guide for Apple Mail gives a settings table whose outgoing row reads “SMTP port, SSL enabled: 587”. That column heading is loose wording, not a third configuration: 587 carries STARTTLS, and the label is describing an encrypted connection rather than the SSL method.
The practical rule is simple. Port 465 opens the TLS session immediately, before any SMTP conversation happens. Port 587 opens in the clear and upgrades on the STARTTLS command. Both end encrypted; they differ in when. Some office networks and residential ISPs block 465 outright, which is exactly the case IONOS describes, and that is when the fallback earns its place. The guide to SSL and TLS in email clients works through the difference in full.
What you must not do is take the port from one page and the encryption label from another. Pairing 587 with SSL rather than STARTTLS produces a handshake failure that no password change will fix, and pairing 465 with STARTTLS produces the mirror image of it. If a server answers only implicit TLS and your client insists on upgrading, you get a refusal of the kind covered in the breakdown of the “must issue a STARTTLS command first” rejection.
Which IONOS Mailbox Do You Have?
IONOS sells mailboxes it operates and mailboxes it resells, and the settings above apply only to the first group. Your address looks identical either way, so check the product on your contract before typing a hostname anywhere.
The mailboxes IONOS runs on its own infrastructure. These are the accounts imap.ionos.com, pop.ionos.com and smtp.ionos.com serve. Everything in the table above describes this product family.
IONOS resells Microsoft Exchange and Microsoft 365. Those mailboxes live on Microsoft infrastructure and take Microsoft hostnames. Nothing on ionos.com applies to them; see the Microsoft 365 mail server settings instead.
IONOS also resells Google Workspace in Business Starter and Business Standard tiers. Same reasoning: Google’s servers, Google’s hostnames, covered in the Google Workspace mail settings reference.
There is a fourth case worth naming, because it drives a steady trickle of searches for 1and1 IMAP settings. IONOS is the rebranded 1&1, and accounts opened under the old name are still live. IONOS documents its mail servers under ionos.com hostnames only, with no legacy entry anywhere in the current help centre. If your client still holds an older hostname and connects, leave it alone; if it fails, replace it with the values in the table rather than hunting for a modern equivalent of the old name. IONOS has not published one.
Setting Up IONOS Email in a Mail Client
The values never change between platforms. What changes is the word each client uses for the same encryption method, and IONOS publishes that mapping itself for the case where you move from 465 to 587. This is the part worth copying carefully.
| Client | Encryption label to select on port 587 |
|---|---|
| Thunderbird | STARTTLS |
| Outlook 2016 and 2019 | TLS |
| Outlook for Microsoft 365 | STARTTLS |
| Gmail app | STARTTLS |
Outlook 2016 and 2019 are the outlier, and it is a naming quirk rather than a protocol difference: those versions label opportunistic TLS as “TLS” and reserve “SSL” for the implicit form on 465. Selecting SSL there while on 587 is the classic IONOS Outlook failure. On iPhone, add the account as “Other” rather than letting Mail guess the provider, and fill in the outgoing server password even where the field is marked optional, since Apple Mail will otherwise send unauthenticated and be refused. On Android, the Gmail app asks for the same three values under Manual setup.
Choosing between the two incoming protocols is a separate decision from choosing a port. IMAP leaves mail on the server and mirrors it to every device, which is what you want on more than one machine; POP3 downloads and, by default, removes. Our walkthroughs of how to configure an IMAP account correctly and what POP3 does to your server copy cover the trade-off, and the general SMTP setup guide covers the outgoing half for any provider. If you would rather not configure anything, IONOS webmail needs no client settings at all, which also makes it the fastest test of whether a failure is credentials or configuration.
Storage and Attachment Limits by Plan
IONOS publishes these in a single table, and the spread across plans is wide enough that a limit quoted for the wrong tier is useless. Values below are as published in August 2026.
| Plan | Mailbox storage | Maximum attachment |
|---|---|---|
| Mail Basic | 2 GB or 100,000 emails | 70 MB |
| Mail Business | 50 GB or 500,000 emails | 70 MB |
| Microsoft Exchange | 50 GB | 100 MB |
| Microsoft 365 Business Basic and Standard | 100 GB or 1 million emails per folder | 150 MB in Outlook, 35 MB in Outlook Web App |
| Google Workspace Business Starter | 30 GB | 25 MB |
| Google Workspace Business Standard | 2 TB | 25 MB |
| Read the condition: IONOS states these attachment ceilings apply when sending from an IONOS mail account to another IONOS mail account of the same type. Send outside that and the receiving provider’s limit governs, which is routinely far lower. A 70 MB attachment is a 70 MB attachment only inside IONOS. | ||
Note also the dual form of the storage limit on the IONOS-operated plans: Mail Basic is capped at 2 GB or 100,000 messages, whichever arrives first. A mailbox full of small messages can hit the count while the gigabyte figure still looks comfortable. If you are weighing these numbers against other providers before committing, the survey of business email hosting services and what they actually include puts them side by side.
The Sending Limits That Break Bulk Mail
This is the section most IONOS settings pages omit, and it is the one that explains the majority of “my settings are correct but mail stopped going out” reports. IONOS applies rate limits at the submission server, and they are tighter than most people expect.
IONOS gives the reason plainly: the restriction exists primarily as a security precaution against spam. The new-package rule is the one that catches people out, because it applies precisely when someone has just bought hosting and is eager to import a list. For five days, a fresh package is held to 50 recipients per six hours no matter which plan it is on.
Two consequences follow. First, a mailbox is not a sending platform: exceeding these thresholds does not produce a clearer error message, it produces deferrals, and a queue of messages deferred for unexpected volume is what a mail client shows you when a rate limit has been reached rather than a setting broken. Second, if you are sending campaigns or transactional mail at all, the outgoing server for that traffic should not be smtp.ionos.com. Route it through a dedicated service and leave the IONOS outgoing mail server for correspondence.
When IONOS Refuses the Connection
IONOS mail servers announce themselves with the Nemesis ESMTP banner, the same mail transfer agent that fronts GMX and WEB.DE, all three being part of the same corporate family. That detail matters for diagnosis, because it means IONOS rejection strings look nothing like the ones Google or Microsoft return, and searching the literal text is often the fastest route to a cause.
The port is blocked before it is wrong. Switch from 465 to 587 and change the encryption label to match, per the table above. This is the exact scenario IONOS documents.
A temporary refusal from the IONOS side rather than a settings fault. The analysis of 421 Nemesis ESMTP Service Not Available covers what triggers it on IONOS, GMX and WEB.DE and what to change.
Almost always the username. IONOS wants the full email address; a client that has helpfully trimmed it to the part before the at sign will fail on an otherwise perfect configuration.
Delivery, not configuration. Read the bounce text against the full list of SMTP error codes and what each one means before touching a single client setting.
One class of problem sits outside the client entirely. If mail leaves fine but nothing arrives, the incoming path is a DNS question rather than an IMAP one: your domain has to point at the IONOS mail servers for anything to be delivered there in the first place, which is what MX records do and how they are read. Redirecting an address to another mailbox is likewise a server-side setting rather than a client one, covered in the guide to how email forwarding is configured.
What IONOS Does Not Publish
Third-party settings pages fill gaps that the provider has left deliberately empty, and the filled-in values are guesses often enough to be worth flagging. As of August 2026, the IONOS help centre publishes no application-specific password scheme for Mail Basic or Mail Business: the mailbox password is the mail client password. It publishes no plaintext incoming hostname, only the encrypted pair. It publishes no daily message ceiling, only the recipient windows quoted above, so a “daily IONOS sending limit” figure has come from somewhere other than IONOS.
Port 25 is the one genuine edge. The IONOS UK glossary names it as a last resort while calling it unsecured and advising against it. It is documented, which is not the same as recommended, and there is no reason to reach for it on a modern client.
Two IONOS neighbours share this architecture and are documented separately on this site, which is useful if you administer more than one of them: the WEB.DE server settings and the access switch they require first follow the same Nemesis lineage with a mandatory extra step that IONOS does not impose.
IONOS Email Settings FAQ
What are the SMTP settings for IONOS?
Outgoing server smtp.ionos.com, port 465 with SSL/TLS, authentication required, username the full email address. If your network blocks 465, IONOS publishes port 587 with STARTTLS as the fallback. Both are official; 465 is the one listed in the IONOS server details table, and 587 is the one its UK glossary recommends.
Is IONOS email POP or IMAP?
Both are offered, on different hostnames. The IONOS IMAP settings are imap.ionos.com on port 993 with SSL/TLS; the IONOS POP3 settings are pop.ionos.com on port 995 with SSL/TLS. Choose IMAP unless you have a specific reason not to, since it keeps mail on the server and syncs across devices, while POP3 downloads and removes by default.
What are the IMAP settings for Outlook on IONOS?
Identical to every other client: imap.ionos.com on 993 with SSL, smtp.ionos.com on 465 with SSL, full address as username. The one Outlook-specific trap is the encryption label if you move to port 587. Outlook 2016 and 2019 call opportunistic encryption “TLS” while Outlook for Microsoft 365 calls it “STARTTLS”, and picking “SSL” on 587 in either will fail the handshake.
Are the IONOS email settings different on iPhone or Android?
No. Hostnames, ports and encryption are the same on every platform, and a page promising special IONOS IMAP settings for iPhone is describing an interface rather than a protocol. On iOS, add the account as “Other” instead of letting Mail detect the provider, and enter the outgoing password even where the field says optional. On Android, use Manual setup in the Gmail app and enter the same three values.
Why did my IONOS email stop sending after a few dozen messages?
A rate limit, not a setting. IONOS allows no more than 100 recipients on one message and no more than 200 within five minutes, asks for a ten second pause between messages, and holds packages under five days old to 50 recipients per six hours. Nothing in your configuration changed; you crossed a threshold. Bulk and campaign traffic belongs on a sending service rather than a mailbox.
Do I need the IONOS webmail settings to log in to webmail?
No. Webmail runs in the browser and configures its own connection, which is why IONOS states that SMTP is set up automatically there. Server details are only required by an external mail program. That makes webmail a useful diagnostic: if it accepts your credentials and a client does not, the problem is in the client configuration rather than the account.
Settings for other business mailbox platforms:
Microsoft 365 Email Settings · Google Workspace Email Settings · Titan Email Settings · Namecheap Private Email Settings
About This Guide
These values were verified on August 28, 2026 against IONOS documentation: its mail server details article for the IMAP, POP3 and SMTP table and the port 587 fallback, its UK SMTP glossary entry for the recommended-port wording and the note on port 25, its Apple Mail setup guide for the “SSL enabled 587” row, its size limitations article for storage and attachment ceilings, and its mass mailing limits article for the recipient thresholds. Where IONOS pages disagree with each other, both readings are quoted rather than reconciled into one. Fields IONOS does not publish, including any application-specific password and any plaintext hostname, are absent rather than filled in from third-party pages. SMTPedia re-verifies provider settings quarterly. If IONOS 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
SMTPedia is an independent email industry reference covering SMTP, IMAP, POP3, email deliverability, marketing platforms, DNS authentication, and email verification. Every article is researched from official provider documentation, IETF RFCs, and industry best practices. Settings and configurations are verified quarterly.
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