Apple, Microsoft Working to Fix iOS 11 Mail App Issues With Outlook.com, Office 365 & Exchange Accounts

Apple says it is working closely with Microsoft to fix an issue that prevents Outlook.com, Office 365, and Exchange 2016 account holders from sending or replying to emails using Apple's native Mail app in iOS 11.

Apple published a support document on Tuesday, September 19 – the official launch date of iOS 11 – to acknowledge the issue affecting users of Microsoft email servers.

ios 11 mail

If you can‘t send an email with iOS 11 and an Outlook.com or Exchange mail account



You might see an error message that says "Cannot Send Mail. The message was rejected by the server."

If your email account is hosted by Microsoft on Outlook.com or Office 365, or an Exchange Server 2016 running on Windows Server 2016, you might see this error message when you try to send an email with iOS 11: "Cannot Send Mail. The message was rejected by the server."

On Tuesday, Microsoft also published a support note, which states that Apple's Mail app in iOS 11 "is not compatible with Outlook.com, Office 365, or Exchange Server 2016 running on Windows Server 2016".

Both companies' statements suggest they were caught off guard by the Mail app problem in iOS 11, however MacRumors is aware of several users who installed beta builds of the mobile operating system and flagged the issue with Apple as far back as July.



Despite apparently being aware of the problems for some time, both Apple and Microsoft said they are still working together to resolve the issue. Apple added that it would release a fix soon in an upcoming software update, while Microsoft offered the following workaround in the meantime.

To work around this issue, download the free Outlook for iOS client from the App Store. The Outlook for iOS client fully supports various email services, including Outlook.com, Office 365, and Exchange Server 2016. 

If you use the Mail app to sync data from Exchange Server 2016 that is running on Windows Server 2016, you can ask the system administrator to disable HTTP/2 in Windows Server 2016 as a workaround. The instructions on disabling HTTP/2 can be found in the Workaround section of KB 4032720: How to deploy custom cipher suite ordering in Windows Server 2016.

Stay tuned to MacRumors to find out as soon as Apple releases a fix for the ongoing Microsoft server issues in iOS 11.

Related Forum: iOS 11

Popular Stories

Apple One Apps Feature 2

Apple One's Best Plan Now Includes Two More Perks For Free

Monday March 10, 2025 6:40 am PDT by
Apple One allows you to subscribe to up to six Apple services for one discounted monthly price. There are three Apple One tiers: Individual, Family, and Premier. Over the last month, the highest-end ‌Apple One‌ Premier plan has gained two additional perks. Here is what Apple One Premier already included, for $37.95 per month:Apple Music Apple TV+ Apple Arcade Apple News+ Apple Fitness+...
Generic iOS 19 Feature Mock Light

iOS 19 Will Bring Biggest Design Overhaul Since iOS 7

Monday March 10, 2025 12:17 pm PDT by
Apple is planning for a major design overhaul of the iPhone, iPad, and Mac interfaces with the introduction of iOS 19, iPadOS 19, and macOS 16 later this year, reports Bloomberg. The update will "fundamentally change" the look of Apple's operating system, introducing a more consistent cross-platform experience. Apple plans to update the style of icons, menus, apps, windows, and system...
2016 12 inch macbook feature

Apple Introduced Its Most Controversial MacBook 10 Years Ago Today

Sunday March 9, 2025 1:00 am PST by
Apple announced the infamous 12-inch Retina MacBook a decade ago today, an experimental new Mac that was as controversial as it was revolutionary. Apple unveiled the 12-inch MacBook on March 9, 2015, at the "Spring Forward" event in San Francisco, California. The event was primarily focused on the Apple Watch, which was being fully detailed ahead of its launch the following month, so the...
iphone 17 mockups idevicehelp

Video Shows iPhone 17 Mockups Based on 'Internal Documents'

Monday March 10, 2025 4:41 am PDT by
YouTuber iDeviceHelp on Friday posted a video that shows off mockups of Apple's forthcoming iPhone 17 models that are purportedly based on "internal documents." We're sharing the video here since it was made in collaboration with leaker Majin Bu, who last month published similar iPhone 17 renders that were widely corroborated by separate leakers with links to Apple's Chinese supply chain....
airpods pro 2 gradient

AirPods Pro 3 Launch Now Just Months Away: Here's What We Know

Tuesday March 11, 2025 3:26 am PDT by
Despite being released over two years ago, Apple's AirPods Pro 2 continue to dominate the wireless earbud market. However, with the AirPods Pro 3 expected to launch in 2025, anyone thinking of buying Apple's premium earbuds may be wondering if the next generation is worth holding out for. Apart from their audio and noise-canceling performance, which are generally regarded as excellent for...
iOS 18

12 New Things Your iPhone Can Do in iOS 18.4

Monday March 10, 2025 9:28 am PDT by
Apple is set to release iOS 18.4 in early April, bringing further refinements to Apple Intelligence features, a neat new capability to iPhone 15 Pro devices, new emoji, and more. While not quite as packed with new features as Apple's preceding iOS 18 point releases, iOS 18.4 still introduces enhancements that aim to make your iPhone smarter and more intuitive. Below, we've listed 12 new...
iOS 18

iOS 18.3.2 Update Coming Soon for iPhones

Monday March 10, 2025 7:25 am PDT by
Apple employees are internally testing iOS 18.3.2 for iPhones, according to our website's visitor logs, which have been a reliable indicator of upcoming iOS versions. The software update should be released in the next week or two. iOS 18.3.2 will be a minor update that addresses software bugs and/or security vulnerabilities. Don't expect any new features. iOS 18.3.2 will be an interim...
iPhone 16 Pro vs iPhone 17 Air Feature

iPhone 17 Air and 17 Pro Max Allegedly Same Size Apart From Thickness

Friday March 7, 2025 2:45 am PST by
Apple's all-new ultra-thin iPhone 17 Air shares the same dimensions as the iPhone 17 Pro Max, with the only difference being in the thickness of the devices, according to the leaker Ice Universe. Posting to their Weibo account, the Chinese leaker today claimed that the iPhone 17 Air and iPhone 17 Pro Max have identical body length, width, screen size, and bezels. "The only difference is the...
iPhone 17 Pro Render Front Page Tech

iPhone 17 Pro Launching Later This Year With These 8 New Features

Tuesday March 4, 2025 3:15 pm PST by
While the iPhone 17 Pro and iPhone 17 Pro Max are not expected to launch until September, there are already plenty of rumors about the devices. iPhone 17 Pro's alleged design via Front Page Tech Below, we recap key changes rumored for the iPhone 17 Pro models as of March 2025: Aluminum frame: iPhone 17 Pro models are rumored to have an aluminum frame, whereas the iPhone 15 Pro and iPhone...

Top Rated Comments

profets Avatar
98 months ago
I could have sworn I saw people complaining about this during the betas. Now, 3 months later and GM released they’re talking about fixing it?
Score: 27 Votes (Like | Disagree)
Phil A. Avatar
98 months ago
I could be wrong, but for me, it seems like more of an Apple problem than a Microsoft one: If it works in iOS 10 (and it does) and doesn't on iOS 11, then the logical conclusion is Apple have changed something in the way they implement the ActiveSync protocol that breaks things
Score: 13 Votes (Like | Disagree)
AFEPPL Avatar
98 months ago
MS :mad:
No, apple made the change - they should have tested the software better or even read the bug reports...!!!
Same happened in the past, it's not like it's unusual.
Score: 9 Votes (Like | Disagree)
srminton Avatar
98 months ago
This is up there with the removal of the AppStore in iTunes. From Mr. Cook's point of view this is a small problem. He probably said, who uses Microsoft products anymore just as he said, who uses the AppStore on the desktop. Both low percentages in his mind.
No, this is false. Compatibility with Microsoft software is important to Apple - that's why they made a big deal of demoing the iPad version of Office. The same is true in reverse for Microsoft, as they have thankfully moved on from the days when they regarded Office as just a tool to force people to use Windows everywhere. MSFT realised that people would just use Google Docs instead, if they didn't make Office great on iOS. Both companies will want this fixed asap.

As for the thing about the app store in iTunes, obviously Apple would have real data about that. It's probably true that very few people use the app store on the desktop, otherwise they wouldn't have removed it. Personally I removed it from the iTunes menu because it was illogical to download mobile phone apps on a desktop when I don't even sync my phone with the desktop. Sure, there will no doubt be a small number of people who were still doing this, just like there were a small number of people using Dashboard widgets or DVD drives. That's just the way it goes, unfortunately, same for Google when they kill services and features, same for Microsoft when they abandoned their phones.
Score: 7 Votes (Like | Disagree)
TheMacDaddy1 Avatar
98 months ago
There were no changes within iOS 11 GM and the official release yesterday. The issue is still happening on tenants within O365 that have HTTP/2 turned on. I had the pleasure of working with Apple and MS over the last 2 weeks sending them logs and other information. You also have to understand, Apple does not use O365 internally or externally so they wouldn't have caught this issue. They have a lot of bug reports that people send in. Most of those users don't even try to troubleshoot by turning it off and back on again. Beta software is supposed to be run on non-production devices. So part of the troubleshooting expecting by Apple is for a restore to be done, eventually. Most people that run the public beta, its on their full time device so many of the bug reports weren't complete and others just didn't work with Apple on the issue. Plus, with everyone saying they sent a bug report, they can't get to everyone who reports a bug.
"You also have to understand, Apple does not use O365 internally or externally so they wouldn't have caught this issue."

I get that they don't use it.

That said I have been managing Exchange servers since the Exchange version 4....24 years ago. When the iPhone first came out it did not have Active Sync support, they wanted Exchange admins to turn on IMAP. It might have happened in a few places but for the most part the iPhone did not work in the corporate world.

Then Apple licensed Active Sync and that was one of the BIG reasons Enterprise adopted the iPhone after that. To not test this thoroughly test Active Sync against Microsoft's email offerings it a mistake on Apple's part. Microsoft still owns the Enterprise Email market and will for a long time. Apple has dumped on the Enterprise market enough over the last 5-10 years. Doing stuff like this only gives those MS fanboys in most Enterpise IT shops more fuel to the "Apple does not do Enterprise" fire. They are probably trying to push some Android option.

This is NOT the first iOS update to break Active Sync support.
Score: 6 Votes (Like | Disagree)
mattynat Avatar
98 months ago
No, apple made the change - they should have tested the software better or even read the bug reports...!!!
Same happened in the past, it's not like it's unusual.
It was actually a Microsoft issue. I was the one working with Apple for my company on this for the past 2 weeks. Microsoft enabled HTTP/2 on their CAFE servers and that caused the issue. I guess its not compatible with iOS 11. It was only happening when you try to send a new email with an attachment or a reply when a signature in the thread had an icon so it attached the icon in the reply. Hope this helps.
[doublepost=1505911674][/doublepost]
Yeah, no problems for me here either. Not sure why I'm not affected, as I'm also using Office 365-hosted corporate email on Mail.app and it's working fine. Actually it's working better than iOS 10, because it has fixed a bug where text would be too small to read on my phone (something to do with HTML, apparently). Now emails are displaying perfectly, and I can send/reply to emails fine too.

I do use the Outlook app for some things, but I prefer Mail.app for quickly scanning email (and because it's the default email app when clicking links). What I really like in iOS 11 is that when I drag an email from Mail.app on my iPad to another app like Notes, Evernote or Things, it creates a link back to the email. This is a killer feature for me, which will keep me on Mail.app.
Its not every O365 tenant. just the ones that Microsoft turned on HTTP/2. They are rolling the affected servers back now. plus, it was only with emails with attachments or replies with a signature with an icon.
Score: 6 Votes (Like | Disagree)