MailCore 2: Introduction

MailCore 2 provides a simple and asynchronous Objective-C API to work with the e-mail protocols IMAP, POP and SMTP. The API has been redesigned from the ground up. It features:

• POP, IMAP and SMTP support
• RFC822 parser and generator
• Asynchronous APIs
• HTML rendering of messages
• iOS and Mac support

Installation

Build for iOS/OSX

Read instructions for iOS/OSX.

Build for Android

Read instructions for Android.

Build for Windows

Read instructions for Windows.

Build for Linux

Read instructions for Linux.

Updating mailcore2 on Windows (Spark prebuilt flow)

Windows builds of spark-core do not compile mailcore2 C++ from source. Build-SparkCore.ps1 clones this repo at a pinned tag and runs build-windows-5.10\Build-SwiftMailcore.ps1, which compiles only the Swift bindings (src/swift) and downloads the prebuilt C++ libraries from S3 (Get-Mailcore2.ps1, mailcore2-all-<N>.zip). Any C++ change reaches Windows only through a new prebuilt archive — merging a PR or moving a tag is not enough.

Prerequisites

Everything below is preinstalled in the CI image ghcr.io/readdle/spark-js-addon-windows-builder — building inside it is the easiest path. On a bare machine you need:

• VS2022 Build Tools with an MSVC toolset whose STL accepts the Swift toolchain's clang. Swift 5.10.1 ships clang 16, so the toolset must be 14.39 (17.9) or older — the 14.40+ STL requires clang 17 and fails with STL1000. Install the side-by-side component Microsoft.VisualStudio.Component.VC.14.39.17.9.x86.x64 and make it the default via VC\Auxiliary\Build\Microsoft.VCToolsVersion.default.txt if a newer toolset is also installed.
• Windows SDK 10.0.18362 (version 1903, from the Windows SDK archive) — the RD build modules pin it when configuring the VS environment.
• RD PowerShell modules (RDBuildCMake, RDBuildMSVC, RDDependency) in PSModulePath.
• Swift 5.10.1 toolchain (provides clang-cl and the Windows SDK with dispatch/BlocksRuntime).
• ICU 69.1 at C:\Library\icu-69.1\usr, libxml2 2.11.5 at C:\Library\libxml2-2.11.5\usr (paths are hardcoded in the script).
• SPARK_PREBUILT_KEY env var — download token for spark-prebuilt-binaries.s3.amazonaws.com (zlib/sasl/openssl prebuilts).
• ssh access to git@github.com:readdle/{ctemplate,libetpan,tidy-html5}.

Build

$env:SPARK_PREBUILT_KEY = "<key>"
powershell -ExecutionPolicy Bypass -File .\build-windows-5.10\Build-Mailcore2.ps1 -Install

The script clones and builds ctemplate/libetpan/tidy, downloads the binary deps, then builds mailcore2/CMailCore with CMake + Ninja using clang-cl from the Swift toolchain. -Install lays the result out in .build\install (bin, include, lib, etc).

• After a failed run, delete .build before retrying — stale CMake caches keep the old configuration (wrong install prefix, wrong build type) and produce confusing errors.
• Verify what was built: type .build\install\etc\mailcore2-git-rev must be the commit you intend to ship.

Package

The zip must contain a single top-level folder named exactly mailcore2-all (that is the path Get-Mailcore2.ps1 extracts):

cd .\.build
Copy-Item -Recurse install mailcore2-all
tar -a -cf mailcore2-all-<N+1>.zip mailcore2-all

Sanity check against the current archive: tar -tf both files and compare the top-level layout.

Upload

The bucket is spark-prebuilt-binaries in eu-central-1. SPARK_PREBUILT_KEY is a download-only token — uploads need real AWS credentials:

aws s3 cp mailcore2-all-<N+1>.zip s3://spark-prebuilt-binaries/mailcore2-all-<N+1>.zip --region eu-central-1

Verify the build can fetch it the same way the script does:

Invoke-RestMethod -Method Head -Uri "https://spark-prebuilt-binaries.s3.amazonaws.com/mailcore2-all-<N+1>.zip" -UserAgent $env:SPARK_PREBUILT_KEY

Never overwrite an existing mailcore2-all-<N>.zip — older tags keep downloading it by name.

Switch builds to the new prebuilt

1. In this repo: bump $PrebuiltMailcoreVersion in build-windows-5.10/Get-Mailcore2.ps1, PR into spark2.
2. Tag the merge with the next 2.1.x tag. The bump must be inside the tag — spark-core runs Get-Mailcore2.ps1 from its mailcore checkout at that tag, so a tag without the bump silently downloads the previous archive.
3. In spark-core-mono, update every mailcore pin to the new tag — the versions must match across platforms:
   • spark-core/build-scripts/Windows-5.10/Build-SparkCore.ps1 (GitBranch of the MailCore dependency) — Windows;
   • spark-core/Package.swift and spark-core/SparkCoreNano/Package.swift (.package(... branch:)) — Mac/Android SPM;
   • spark-js-addon/scripts/mac/configure.rb (RemoteSwiftPackage) — the source the addon workspace is generated from;
   • spark-js-addon/SparkCoreAddon.xcworkspace/xcshareddata/swiftpm/Package.resolved — autogenerated from configure.rb but tracked in git; update the branch/revision pair so CI resolves without a regeneration step.

Local testing without a prebuilt

To test unreleased C++ changes, add -BuildMailcore2 to the Build-SwiftMailcore.ps1 invocation in Build-SparkCore.ps1 — mailcore2 is then compiled from the pinned checkout instead of downloading the archive. Slower (~10–15 min extra), for test builds only; remove it before release.

Basic IMAP Usage

Using MailCore 2 is just a little more complex conceptually than the original MailCore. All fetch requests in MailCore 2 are made asynchronously through a queue. What does this mean? Well, let's take a look at a simple example:

    MCOIMAPSession *session = [[MCOIMAPSession alloc] init];
    [session setHostname:@"imap.gmail.com"];
    [session setPort:993];
    [session setUsername:@"ADDRESS@gmail.com"];
    [session setPassword:@"123456"];
    [session setConnectionType:MCOConnectionTypeTLS];

    MCOIMAPMessagesRequestKind requestKind = MCOIMAPMessagesRequestKindHeaders;
    NSString *folder = @"INBOX";
    MCOIndexSet *uids = [MCOIndexSet indexSetWithRange:MCORangeMake(1, UINT64_MAX)];

    MCOIMAPFetchMessagesOperation *fetchOperation = [session fetchMessagesOperationWithFolder:folder requestKind:requestKind uids:uids];

    [fetchOperation start:^(NSError * error, NSArray * fetchedMessages, MCOIndexSet * vanishedMessages) {
        //We've finished downloading the messages!

        //Let's check if there was an error:
        if(error) {
            NSLog(@"Error downloading message headers:%@", error);
        }

        //And, let's print out the messages...
        NSLog(@"The post man delivereth:%@", fetchedMessages);
    }];

In this sample, we retrieved and printed a list of email headers from an IMAP server. In order to execute the fetch, we request an asynchronous operation object from the MCOIMAPSession instance with our parameters (more on this later). This operation object is able to initiate a connection to Gmail when we call the start method. Now here's where things get a little tricky. We call the start function with an Objective-C block, which is executed on the main thread when the fetch operation completes. The actual fetching from IMAP is done on a background thread, leaving your UI and other processing free to use the main thread.

Documentation

• Class documentation Obj-C / Java
• Wiki

License

MailCore 2 is BSD-Licensed.