If you’ve ever tried to set up a third-party email account in the Outlook mobile app and hit a wall, you’re not alone. One of the most common errors users encounter is:
“Error: IMAP Secure Connection Not Available. Your email service provider does not provide the option of logging in using a secure connection for IMAP. You may login using an insecure connection.”
The frustrating part? Your business email hosting provider almost certainly does support secure IMAP — and you can prove it by setting up the same account in Apple Mail, Gmail, or virtually any other email client without issue.
So what’s going on?
The Problem Isn’t Your Email Provider
Microsoft has acknowledged this error in their official support documentation, but the page offers little explanation and no real solution — which tells you something about the nature of the issue.
The reality is that Outlook mobile wasn’t designed to be a general-purpose email client. It was built from the ground up for Microsoft Exchange and Microsoft 365 accounts, and standard IMAP support has always been a secondary consideration.
How Outlook Mobile Actually Works
Unlike traditional email apps that connect directly to your mail server via IMAP, Outlook mobile takes a different approach. When Microsoft acquired the email app Acompli in 2014, they inherited an architecture that routes email through Microsoft’s cloud infrastructure rather than connecting directly to mail servers.
As Practical365 explains, Outlook mobile fetches and caches mailbox content through Azure, enabling advanced features like the Focused Inbox. This works beautifully for Exchange accounts but creates compatibility issues with standard IMAP servers that don’t integrate with Microsoft’s authentication systems.
This architectural choice has real consequences. In Microsoft’s own Q&A forums, support staff have confirmed that “Outlook Mobile switches from IMAP to OAuth and Exchange ActiveSync” when it detects certain account types — sometimes even when users explicitly want to use IMAP.
The Evidence Is Everywhere
Browse any email-related support forum and you’ll find users experiencing the same issues:
- Accounts that worked for years suddenly stop: One user reported that their IMAP email “worked for past 10 years” before Outlook mobile suddenly couldn’t connect. Even Microsoft’s own mobile support team couldn’t resolve it.
- IMAP setup options disappearing: Users on Microsoft’s Q&A forums report that the app forces them into Microsoft’s authentication flow even when they’re trying to add a standard IMAP account, with one frustrated user noting “IT IS NOT POSSIBLE TO CHOOSE IMAP FIRST.”
- Privacy concerns: Contributors in Apple’s support community have pointed out that Outlook “diverts all of your emails and stores them on Microsoft servers” rather than connecting directly to your mail server — a significant consideration for users of third-party email hosting.
Microsoft’s own troubleshooting documentation acknowledges that “if you set up your email as an IMAP or POP account, your calendars and contacts won’t sync.” This is where open standards actually shine — with CalDAV and CardDAV sync, you can keep your calendar and contacts in sync across devices without being locked into Microsoft’s ecosystem.
If You Still Want to Try Outlook Mobile
For IMAP accounts that do work with Outlook mobile, here are the settings you should use for a secure IMAP connection:
Incoming Mail (IMAP)
- Server: Your provider’s IMAP server (e.g., secure.greatmail.com)
- Port: 993
- Encryption: SSL/TLS
Outgoing Mail (SMTP)
- Server: Your provider’s SMTP server (e.g., secure.greatmail.com)
- Port: 465
- Encryption: SSL/TLS
When adding the account, look for “Advanced Settings” or “Other account (IMAP)” options — though as noted above, these options aren’t always available depending on your app version and how Outlook interprets your email address.
Better Alternatives for IMAP Email
If you’re using small business email from a third-party hosting provider and need reliable mobile access, you’re better served by email apps designed to work with standard protocols rather than fighting Outlook’s Exchange-first architecture.
Apps that handle IMAP connections reliably include:
- Native mail apps: Apple Mail (iOS) and Samsung Email (Android) both offer solid IMAP support with proper push notifications and calendar/contact sync via CalDAV/CardDAV.
- Spark: Excellent for team collaboration with shared inboxes and real-time collaborative drafting. Works seamlessly with any IMAP provider.
- Edison Mail: Known for speed and smart inbox features. Consistently ranked among the fastest for fetching new messages.
- BlueMail: Great for users juggling multiple accounts across different providers.
- Thunderbird Mobile: The mobile companion to the popular desktop client. If you’re already using Thunderbird with TbSync on your computer, this provides a consistent experience across devices.
For a deeper look at these options, see our guide to Best Mobile Email Apps for Business.
The Bottom Line
The Outlook mobile app is a powerful tool — for Microsoft accounts. If you’re using Exchange, Microsoft 365, or Outlook.com email, it’s hard to beat. But for users of independent email hosting providers who rely on standard IMAP, the app’s architectural decisions create unnecessary friction.
If you’re seeing “IMAP Secure Connection Not Available” or similar errors, the problem likely isn’t your email provider’s security settings — it’s that Outlook mobile wasn’t built with your use case as a priority. Save yourself the troubleshooting headache and choose an email app designed to work with open standards.
Using Greatmail for your business email? Our servers fully support secure IMAP (port 993) and SMTP (port 465) connections. If you’re having trouble with any email client, contact our support team — we’re happy to help you get connected.