diff --git a/.cirrus.yml b/.cirrus.yml
deleted file mode 100644
index eab595f..0000000
--- a/.cirrus.yml
+++ /dev/null
@@ -1,22 +0,0 @@
-task:
-  name: freebsd-stable
-  freebsd_instance:
-    image_family: freebsd-12-1
-  env:
-    RUST_BACKTRACE: 1
-  setup_script:
-    - pkg install -y curl git
-    - curl https://sh.rustup.rs -sSf --output rustup.sh
-    - sh rustup.sh -y
-    - . $HOME/.cargo/env
-  check_script:
-    - . $HOME/.cargo/env
-    - cargo check --all-targets --all-features
-  build_script:
-    - . $HOME/.cargo/env
-    - cargo build --all-targets --verbose --all-features
-  test_script:
-    - . $HOME/.cargo/env
-    - cargo test --examples --all-features
-    - cargo test --doc --all-features
-    - cargo test --lib --all-features
diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
new file mode 100644
index 0000000..3675f66
--- /dev/null
+++ b/.github/workflows/coverage.yml
@@ -0,0 +1,34 @@
+on:
+  push:
+    branches: [master]
+  pull_request:
+name: coverage
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    container:
+      image: xd009642/tarpaulin
+      options: --security-opt seccomp=unconfined
+    steps:
+      - uses: actions/checkout@v2
+      - name: Generate code coverage
+        run: |
+          cargo tarpaulin --verbose --timeout 120 --out Xml
+        env:
+          TEST_HOST: greenmail
+      - name: Upload to codecov.io
+        uses: codecov/codecov-action@v2
+        with:
+          fail_ci_if_error: true
+    services:
+      greenmail:
+        image: greenmail/standalone:1.6.3
+        ports:
+          - 3025:3025
+          - 3110:3110
+          - 3143:3143
+          - 3465:3465
+          - 3993:3993
+          - 3995:3995
+        env:
+          GREENMAIL_OPTS: "-Dgreenmail.setup.test.all -Dgreenmail.hostname=0.0.0.0 -Dgreenmail.auth.disabled -Dgreenmail.verbose"
diff --git a/.github/workflows/features.yml b/.github/workflows/features.yml
new file mode 100644
index 0000000..dd787cb
--- /dev/null
+++ b/.github/workflows/features.yml
@@ -0,0 +1,25 @@
+on:
+  push:
+    branches: [master]
+  pull_request:
+name: cargo hack
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+      - uses: actions/checkout@v2
+      - name: Install cargo-hack
+        uses: actions-rs/install@v0.1
+        with:
+          crate: cargo-hack
+          version: latest
+          use-tool-cache: true
+      - name: cargo hack
+        uses: actions-rs/cargo@v1
+        with:
+          command: hack
+          args: --feature-powerset check --all-targets
diff --git a/.github/workflows/minimal.yml b/.github/workflows/minimal.yml
new file mode 100644
index 0000000..753211e
--- /dev/null
+++ b/.github/workflows/minimal.yml
@@ -0,0 +1,40 @@
+on:
+  push:
+    branches: [master]
+  pull_request:
+name: With dependencies at minimal versions
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+      - uses: actions/checkout@v2
+      - name: cargo update -Zminimal-versions
+        uses: actions-rs/cargo@v1
+        with:
+          command: update
+          toolchain: nightly
+          args: -Zminimal-versions
+      - name: cargo test
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+    services:
+      greenmail:
+        image: greenmail/standalone:1.6.3
+        ports:
+          - 3025:3025
+          - 3110:3110
+          - 3143:3143
+          - 3465:3465
+          - 3993:3993
+          - 3995:3995
+        env:
+          GREENMAIL_OPTS: "-Dgreenmail.setup.test.all -Dgreenmail.hostname=0.0.0.0 -Dgreenmail.auth.disabled -Dgreenmail.verbose"
diff --git a/.github/workflows/msrv.yml b/.github/workflows/msrv.yml
new file mode 100644
index 0000000..90a3a69
--- /dev/null
+++ b/.github/workflows/msrv.yml
@@ -0,0 +1,19 @@
+on:
+  push:
+    branches: [master]
+  pull_request:
+name: Minimum Supported Rust Version
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: 1.46.0 # bitflags requires 1.46+
+          override: true
+      - uses: actions/checkout@v2
+      - name: cargo +1.46.0 check
+        uses: actions-rs/cargo@v1
+        with:
+          command: check
diff --git a/.github/workflows/os-check.yml b/.github/workflows/os-check.yml
new file mode 100644
index 0000000..bbcb475
--- /dev/null
+++ b/.github/workflows/os-check.yml
@@ -0,0 +1,24 @@
+on:
+  push:
+    branches: [master]
+  pull_request:
+name: cargo check
+jobs:
+  os-check:
+    runs-on: ${{ matrix.os }}
+    name: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [macos-latest, windows-latest]
+    steps:
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+      - uses: actions/checkout@v2
+      - name: cargo check
+        uses: actions-rs/cargo@v1
+        with:
+          command: check
+          args: --all-features --all-targets
diff --git a/.github/workflows/style.yml b/.github/workflows/style.yml
new file mode 100644
index 0000000..34c058e
--- /dev/null
+++ b/.github/workflows/style.yml
@@ -0,0 +1,36 @@
+on:
+  push:
+    branches: [master]
+  pull_request:
+name: lint
+jobs:
+  style:
+    runs-on: ubuntu-latest
+    name: ${{ matrix.toolchain }}
+    strategy:
+      fail-fast: false
+      matrix:
+        toolchain: [stable, beta]
+    steps:
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: ${{ matrix.toolchain }}
+          components: rustfmt, clippy
+      - uses: actions/checkout@v2
+      - name: cargo fmt --check
+        uses: actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --check
+      - name: cargo doc
+        uses: actions-rs/cargo@v1
+        if: always()
+        with:
+          command: doc
+          args: --no-deps --all-features
+      - name: cargo clippy
+        uses: actions-rs/clippy-check@v1
+        if: always()
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..5c862d5
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,34 @@
+on:
+  push:
+    branches: [master]
+  pull_request:
+name: cargo test
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    name: ${{ matrix.toolchain }}
+    strategy:
+      matrix:
+        toolchain: [stable, beta, nightly]
+    steps:
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: ${{ matrix.toolchain }}
+      - uses: actions/checkout@v2
+      - name: cargo test
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+    services:
+      greenmail:
+        image: greenmail/standalone:1.6.3
+        ports:
+          - 3025:3025
+          - 3110:3110
+          - 3143:3143
+          - 3465:3465
+          - 3993:3993
+          - 3995:3995
+        env:
+          GREENMAIL_OPTS: "-Dgreenmail.setup.test.all -Dgreenmail.hostname=0.0.0.0 -Dgreenmail.auth.disabled -Dgreenmail.verbose"
diff --git a/Cargo.toml b/Cargo.toml
index caa9fc7..91f544d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -21,7 +21,7 @@ default = ["native-tls"]
 native-tls = { version = "0.2.2", optional = true }
 rustls-connector = { version = "0.13.1", optional = true }
 regex = "1.0"
-bufstream = "0.1"
+bufstream = "0.1.3"
 imap-proto = "0.14.1"
 nom = { version = "6.0", default-features = false }
 base64 = "0.13"
@@ -30,11 +30,17 @@ lazy_static = "1.4"
 ouroboros = "0.9.5"
 
 [dev-dependencies]
-lettre = "0.9"
-lettre_email = "0.9"
+lettre = "0.9.2"
+lettre_email = "0.9.2"
 rustls-connector = "0.13.0"
 structopt = "0.3"
 
+# to make -Zminimal-versions work
+encoding = "0.2.32"
+hostname = "0.1.3"
+failure = "0.1.8"
+mime = "0.3.4"
+
 [[example]]
 name = "basic"
 required-features = ["default"]
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
deleted file mode 100644
index b7a422d..0000000
--- a/azure-pipelines.yml
+++ /dev/null
@@ -1,109 +0,0 @@
-jobs:
- - job: test
-   displayName: cargo test --{examples,doc,lib}
-   strategy:
-     matrix:
-       Linux-stable:
-         vmImage: ubuntu-latest
-         rust: stable
-       Linux-beta:
-         vmImage: ubuntu-latest
-         rust: beta
-       Linux-nightly:
-         vmImage: ubuntu-latest
-         rust: nightly
-       MacOS:
-         vmImage: macOS-10.14
-         rust: stable
-       Windows:
-         vmImage: windows-2019
-         rust: stable
-   continueOnError: $[eq(variables.rust, 'nightly')]
-   pool:
-     vmImage: $(vmImage)
-   steps:
-     - template: install-rust.yml@templates
-       parameters:
-         rust: $(rust)
-     - script: cargo check --all-targets --all-features
-       displayName: cargo check
-     - script: cargo test --examples --all-features
-       displayName: cargo test --examples
-     - script: cargo test --doc --all-features
-       displayName: cargo test --doc
-     - script: cargo test --lib --all-features
-       displayName: cargo test --lib
-     - script: |
-         set -e
-         rustup component add rustfmt
-         cargo fmt --all -- --check
-       displayName: cargo fmt --check
-       condition: and(eq( variables['rust'], 'beta' ), eq( variables['Agent.OS'], 'Linux' ))
-     - script: |
-         set -e
-         rustup component add clippy
-         cargo clippy -- -D warnings
-       displayName: cargo clippy
-       condition: and(eq( variables['rust'], 'beta' ), eq( variables['Agent.OS'], 'Linux' ))
- # This represents the minimum Rust version supported.
- # Tests are not run as tests may require newer versions of rust.
- - job: msrv
-   pool:
-     vmImage: ubuntu-latest
-   displayName: "Minimum supported Rust version: 1.46.0"
-   dependsOn: []
-   steps:
-     - template: install-rust.yml@templates
-       parameters:
-         rust: 1.46.0 # bitflags requires 1.46+
-     - script: cargo check
-       displayName: cargo check
- - job: integration
-   displayName: cargo test --tests
-   pool:
-     vmImage: ubuntu-latest
-   services:
-     greenmail: greenmail
-   steps:
-     - template: install-rust.yml@templates
-     - script: cargo test --tests
-       displayName: cargo test
- - template: coverage.yml@templates
-   parameters:
-     token: $(CODECOV_TOKEN_SECRET)
-     services:
-       greenmail: greenmail
-     env:
-       TEST_HOST: greenmail
- - job: features
-   displayName: "Check feature combinations"
-   pool:
-     vmImage: ubuntu-latest
-   steps:
-     - template: install-rust.yml@templates
-       parameters:
-         rust: stable
-     - script: cargo install cargo-hack
-       displayName: install cargo-hack
-     - script: cargo hack --feature-powerset check --all-targets
-       displayName: cargo hack
-
-resources:
-  repositories:
-    - repository: templates
-      type: github
-      name: crate-ci/azure-pipelines
-      ref: refs/heads/v0.4
-      endpoint: jonhoo
-  containers:
-   - container: greenmail
-     image: greenmail/standalone:1.6.3
-     ports:
-       - 3025:3025
-       - 3110:3110
-       - 3143:3143
-       - 3465:3465
-       - 3993:3993
-       - 3995:3995
-     env:
-       GREENMAIL_OPTS: "-Dgreenmail.setup.test.all -Dgreenmail.hostname=0.0.0.0 -Dgreenmail.auth.disabled -Dgreenmail.verbose"