Error in downloading mail on IMAP after ios 18 upgrade

Hi All,

I'm experiencing the same problem. No personal IMAP or POP3 accounts work, even though the SSL and TLS certificates are fine.

This is a very big problem. If Apple doesn't fix it quickly, I might go back to iOS 17 or switch to another brand.

I believe that for Apple and its development team, it should be quite simple to fix an issue like this, and I find it very concerning that a solution hasn't been provided yet. After all, what complex code could be behind a function you've been implementing for over 10 years? I strongly urge you to resolve this quickly, or many of us will be forced to leave a platform that has so far been both reliable and secure.

Thank you.

The case finally landed in Cupertino! We have a case no. and the developer are in the process of analyzing the problem and implementing a solution. It is a bug that will be fixed in one of the next releases. As soon as I have news I will post them...

I am getting POSIX error 54 when checking my iCloud email. It’s been working fine since the iOS 18 launch until today.

Is there any current information on this?

Even the latest update to iOS 18.1 has not fixed the error.

My understanding is IMAP server (dovcot) returning some kind of message which Mail app returning as POSIX 96. in my case i have iRedMail setup which uses dovecot to provide IMAP and that dovecot having the facility to record the each login time to mysql database. In that i had issue in that table mysql not able to update lastlogin details. the error is return to IMAP client (Mail app) and Mail app showing that as error. usually all other IMAP client apps will ignore this type of IMAP protocol replies and continue to do service. But iOS18 Mail app stopping at these type of un-handled error messages in IMAP communication.

So my guess is, 1) Your dovecot server also having such issue and returning un-supported/un-handled error reply to IMAP client. if you are running your dovecot in debug mode, you can find the issue and fix it. Then your iOS18 Mail app will work.

2) Apple also can improve the IMAP protocol handling in their upcoming Mail app releases like if such type of ignorable error coming from IMAP server, simply ignore it by showing warning or do no action and do the mail fetch and do the essential operation.

I have plan to reproduce this error in my server maintenance time. if i am able to reproduce it, i will update about the specific protocol error that may help apple/others to fix the issue.

I did some more testing and I isolated the problem. On my Dovecot servers that iOS devices cannot connect to, the folder hierarchy separator is set to "\\" (an escaped backslash). On the one that I could still connect to the separator is set to ".". I created a test server (v2.3.17) and confirmed that iOS will not connect with a backslash, changing this to pretty much anything else (".", "/", "|") allows iOS to connect again, set it back to a backslash and it fails.

Unfortunately it's not trivial to change the separator for existing Dovecot installations, but that's apparently what's causing the Mail app to choke.

Using a backslash is not uncommon and is what Outlook servers generally do, so this is not an unusual situation (I use it because it allows "." and "/" in folder names).

Hopefully Apple will fix this regression soon.

FWIW, not fixed in 18.1

This may not be the Mail App issue, When i got new iPhone with iOS18, i got the same issue after the migration and even i deleted the account and recreated in Mail app, it did not worked. Then i have checked my server about the dovecot error log and i noticed that its had issue in keeping the authentication session and i fixed it, then Mail app started getting message and its not showed any error related to POSIX 96 till now.

On my desktop Mac I had no issue with BT emails so it’s got to be an incompatibility issue with OIS 18 & their own email client / which needs a fix asap !

Looking at this thread it's fairly obvious that there are several different issues going on here. If deleting and recreating your mail account settings are fixing this, you had a configuration error. If using or not using a VPN is fixing this, you have a networking issue. If you're having a problem with a POP account, that's something else entirely. If the problem is intermittent, it's something else again.

In my case, and I believe many others here, the issue is a bug in Mail that was introduced in iOS 18 dealing with the IMAP folder separator character.

During the initial IMAP handshake, the server tells the client which character is used to separate paths for nested mailbox folders. e.g. If you have a mailbox 'Bills' with a mailbox 'Electric' in it, the path to that folder may be '/Bills/Electric', or '\Bills\Electric', or '.Bills.Electric', using whatever separator character the server prefers. There is no standard character used, but those three are the most common.

The caveat is that whatever character is used as a folder separator, can't exist in a mailbox name, so using '\' is fairly common as it frees '/' and '.' for use in mailbox names. Unfortunately, backslashes are also commonly used as escapes, and I suspect the IMAP code in Mail had a regression where a '\' character is getting misinterpreted as an escape during the IMAP handshake, causing an error and the client to drop the connection.

I'm running several Dovecot servers, some using '\' and some using '/'. iOS Mail fails on all the ones using '\', the ones using '/' work fine. Same version of Dovecot on the same server OS, all other Dovecot configuration is identical. When the client drops the connection, it's always immediately after the initial handshake, and there are no errors in the server logs. Even with debugging turned all the way up.

Those here running their own server, I'd like to hear what your folder separator is set to. If you change it to anything else, I expect your connection problems will go away.

Note that changing the folder separator has its own risks, Dovecot recommends you never change it. If any user has a mailbox name containing the new separator, their client (and possibly your server, depending on how the mail is stored on disk) will get confused (you'll see a single mailbox turn into one nested inside another). You also may break mail filters among other things. Make this change at your own risk. If you have the means, it's safer to stand up a new server with a different separator character, and then migrate the mail to it using an IMAP client.

Ideally, of course, Apple acknowledges and fixes the bug.

I’m getting the same problem, but I had this problem way before IOS 18.

I have Hotmail as my main email account—have for decades. Lately, the mail app on my iPhone Willy Nilly decides my password is incorrect and stops receiving and sending mail. I use the same password I have been using since I changed it earlier this year and sometimes it gets my mail working and sometimes it doesn’t. Oddly enough, the mail app on my iPad doesn’t behave this way, logging on to Outlook via a browser to access my mail doesn’t have a problem—it’s just on my phone mail app. I’m at a loss as to how to fix this. Any help would be greatly appreciated. 

I’m getting: Network Error POSIX 96 

Same issue, on iPhone and iPad, started with upgrade to iOS 18, not fixed with 18.0.1.

I can access the same accounts fine from a desktop MacOS Mail app.

Dovecot (v2.3.20) debug logs show a successful TLS connection and authentication, opening the INBOX, executing LIST, then immediately disconnecting. No errors reported on the server side.

I also run a slightly older version of Dovecot (v2.3.17) on another server and my iOS devices can get mail just fine. I'm wondering if the iOS 18 clients are doing something slightly non-standard causing newer Dovecot versions to close the connection.