diff --git a/README.md b/README.md
index b6f000f672..d691e01e61 100644
--- a/README.md
+++ b/README.md
@@ -166,8 +166,9 @@ FairEmail uses:
 * [ShortcutBadger](https://github.com/leolin310148/ShortcutBadger). Copyright 2014 Leo Lin. [Apache license](https://github.com/leolin310148/ShortcutBadger/blob/master/LICENSE).
 * [PhotoView](https://github.com/chrisbanes/PhotoView). Copyright 2018 Chris Banes. [Apache License](https://github.com/chrisbanes/PhotoView/blob/master/LICENSE).
 * [Bugsnag exception reporter for Android](https://github.com/bugsnag/bugsnag-android). Copyright (c) 2012 Bugsnag. [MIT License](https://github.com/bugsnag/bugsnag-android/blob/master/LICENSE.txt).
+* [biweekly](https://github.com/mangstadt/biweekly). Copyright (c) 2013-2018, Michael Angstadt. [BSD 2-Clause](https://github.com/mangstadt/biweekly/blob/master/LICENSE).
 
-FairEmail is sponsored by:
+Error reporting is sponsored by:
 
 ![Bugsnag Logo](/images/bugsnag_logo_navy.png)
 
diff --git a/app/build.gradle b/app/build.gradle
index 7fba83524a..1d23c43efa 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -133,6 +133,7 @@ dependencies {
     def badge_version = "1.1.22"
     def photoview_version = "2.3.0"
     def bugsnag_version = "4.14.0"
+    def biweekly_version = "0.6.3"
 
     // https://developer.android.com/jetpack/androidx/releases/
 
@@ -217,6 +218,11 @@ dependencies {
     // https://github.com/bugsnag/bugsnag-android
     implementation "com.bugsnag:bugsnag-android:$bugsnag_version"
 
+    // https://github.com/mangstadt/biweekly
+    implementation("net.sf.biweekly:biweekly:$biweekly_version") {
+        exclude group: 'com.fasterxml.jackson.core', module: 'jackson-core'
+    }
+
     // git clone https://android.googlesource.com/platform/frameworks/opt/colorpicker
     implementation project(path: ':colorpicker')
 }
diff --git a/app/src/main/java/eu/faircode/email/AdapterMessage.java b/app/src/main/java/eu/faircode/email/AdapterMessage.java
index f8f96c252c..bd9187c63a 100644
--- a/app/src/main/java/eu/faircode/email/AdapterMessage.java
+++ b/app/src/main/java/eu/faircode/email/AdapterMessage.java
@@ -121,6 +121,13 @@ import java.util.List;
 import javax.mail.Address;
 import javax.mail.internet.InternetAddress;
 
+import biweekly.Biweekly;
+import biweekly.ICalendar;
+import biweekly.component.VEvent;
+import biweekly.property.Attendee;
+import biweekly.property.Summary;
+import biweekly.util.ICalDate;
+
 public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHolder> {
     private Context context;
     private LayoutInflater inflater;
@@ -253,10 +260,17 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
         private ContentLoadingProgressBar pbBody;
         private TextView tvNoInternetBody;
 
+        private TextView tvCalendarSummary;
+        private TextView tvCalendarStart;
+        private TextView tvCalendarEnd;
+        private TextView tvAttendees;
+        private ContentLoadingProgressBar pbCalendarWait;
+
         private RecyclerView rvImage;
 
         private Group grpAddresses;
         private Group grpHeaders;
+        private Group grpCalendar;
         private Group grpAttachments;
         private Group grpImages;
 
@@ -333,6 +347,13 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
             pbHeaders = itemView.findViewById(R.id.pbHeaders);
             tvNoInternetHeaders = itemView.findViewById(R.id.tvNoInternetHeaders);
 
+            tvCalendarSummary = view.findViewById(R.id.tvCalendarSummary);
+            tvCalendarStart = view.findViewById(R.id.tvCalendarStart);
+            tvCalendarEnd = view.findViewById(R.id.tvCalendarEnd);
+            tvAttendees = view.findViewById(R.id.tvAttendees);
+
+            pbCalendarWait = view.findViewById(R.id.pbCalendarWait);
+
             rvAttachment = attachments.findViewById(R.id.rvAttachment);
             rvAttachment.setHasFixedSize(false);
             LinearLayoutManager llm = new LinearLayoutManager(context);
@@ -367,6 +388,7 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
 
             grpAddresses = itemView.findViewById(R.id.grpAddresses);
             grpHeaders = itemView.findViewById(R.id.grpHeaders);
+            grpCalendar = itemView.findViewById(R.id.grpCalendar);
             grpAttachments = attachments.findViewById(R.id.grpAttachments);
             grpImages = itemView.findViewById(R.id.grpImages);
         }
@@ -693,6 +715,7 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
 
             grpAddresses.setVisibility(View.GONE);
             grpHeaders.setVisibility(View.GONE);
+            grpCalendar.setVisibility(View.GONE);
             grpAttachments.setVisibility(View.GONE);
             grpImages.setVisibility(View.GONE);
 
@@ -724,6 +747,12 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
             pbHeaders.setVisibility(View.GONE);
             tvNoInternetHeaders.setVisibility(View.GONE);
 
+            tvCalendarSummary.setVisibility(View.GONE);
+            tvCalendarStart.setVisibility(View.GONE);
+            tvCalendarEnd.setVisibility(View.GONE);
+            tvAttendees.setVisibility(View.GONE);
+            pbCalendarWait.setVisibility(View.GONE);
+
             cbInline.setVisibility(View.GONE);
             btnDownloadAttachments.setVisibility(View.GONE);
             btnSaveAttachments.setVisibility(View.GONE);
@@ -997,6 +1026,7 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
             boolean download = false;
             boolean save = (attachments.size() > 1);
             boolean downloading = false;
+            boolean calendar = false;
             List<EntityAttachment> a = new ArrayList<>();
             for (EntityAttachment attachment : attachments) {
                 boolean inline = (TextUtils.isEmpty(attachment.name) ||
@@ -1011,9 +1041,92 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
                     downloading = true;
                 if (show_inline || !inline)
                     a.add(attachment);
+
+                if (attachment.available && "text/calendar".endsWith(attachment.type)) {
+                    // https://tools.ietf.org/html/rfc5546
+                    calendar = true;
+
+                    Bundle args = new Bundle();
+                    args.putSerializable("file", attachment.getFile(context));
+
+                    new SimpleTask<ICalendar>() {
+                        @Override
+                        protected void onPreExecute(Bundle args) {
+                            grpCalendar.setVisibility(View.VISIBLE);
+                            pbCalendarWait.setVisibility(View.VISIBLE);
+                        }
+
+                        @Override
+                        protected void onPostExecute(Bundle args) {
+                            pbCalendarWait.setVisibility(View.GONE);
+                        }
+
+                        @Override
+                        protected ICalendar onExecute(Context context, Bundle args) throws IOException {
+                            File file = (File) args.getSerializable("file");
+                            return Biweekly.parse(file).first();
+                        }
+
+                        @Override
+                        protected void onExecuted(Bundle args, ICalendar icalendar) {
+                            if (icalendar == null || icalendar.getEvents().size() == 0)
+                                return;
+
+                            DateFormat df = SimpleDateFormat.getDateTimeInstance();
+
+                            VEvent event = icalendar.getEvents().get(0);
+
+                            Summary summary = event.getSummary();
+
+                            ICalDate start = event.getDateStart() == null ? null : event.getDateStart().getValue();
+                            ICalDate end = event.getDateEnd() == null ? null : event.getDateEnd().getValue();
+
+                            List<String> attendee = new ArrayList<>();
+                            for (Attendee a : event.getAttendees()) {
+                                String email = a.getEmail();
+                                String name = a.getCommonName();
+                                if (TextUtils.isEmpty(name)) {
+                                    if (!TextUtils.isEmpty(email))
+                                        attendee.add(email);
+                                } else {
+                                    if (TextUtils.isEmpty(email) || name.equals(email))
+                                        attendee.add(name);
+                                    else
+                                        attendee.add(name + " (" + email + ")");
+                                }
+                            }
+
+                            tvCalendarSummary.setText(summary == null ? null : summary.getValue());
+                            tvCalendarSummary.setVisibility(summary == null ? View.GONE : View.VISIBLE);
+
+                            tvCalendarStart.setText(start == null ? null : df.format(start.getTime()));
+                            tvCalendarStart.setVisibility(start == null ? View.GONE : View.VISIBLE);
+
+                            tvCalendarEnd.setText(end == null ? null : df.format(end.getTime()));
+                            tvCalendarEnd.setVisibility(end == null ? View.GONE : View.VISIBLE);
+
+                            tvAttendees.setText(TextUtils.join(", ", attendee));
+                            tvAttendees.setVisibility(attendee.size() == 0 ? View.GONE : View.VISIBLE);
+                        }
+
+                        @Override
+                        protected void onException(Bundle args, Throwable ex) {
+                            Helper.unexpectedError(context, owner, ex);
+                        }
+                    }.execute(context, owner, args, "message:calendar");
+                }
             }
             adapterAttachment.set(a);
 
+            if (!calendar) {
+                tvCalendarSummary.setVisibility(View.GONE);
+                tvCalendarStart.setVisibility(View.GONE);
+                tvCalendarEnd.setVisibility(View.GONE);
+                tvAttendees.setVisibility(View.GONE);
+                pbCalendarWait.setVisibility(View.GONE);
+                grpCalendar.setVisibility(View.GONE);
+            }
+
             cbInline.setOnCheckedChangeListener(null);
             cbInline.setChecked(show_inline);
             cbInline.setVisibility(has_inline ? View.VISIBLE : View.GONE);
diff --git a/app/src/main/res/layout/include_message_calendar.xml b/app/src/main/res/layout/include_message_calendar.xml
new file mode 100644
index 0000000000..4b0221efc8
--- /dev/null
+++ b/app/src/main/res/layout/include_message_calendar.xml
@@ -0,0 +1,98 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    tools:context=".ActivityView">
+
+    <View
+        android:id="@+id/vSeparatorCalendar"
+        android:layout_width="0dp"
+        android:layout_height="1dp"
+        android:layout_marginStart="6dp"
+        android:layout_marginTop="3dp"
+        android:layout_marginEnd="6dp"
+        android:background="?attr/colorSeparator"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent" />
+
+    <TextView
+        android:id="@+id/tvCalendarSummary"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:layout_marginStart="6dp"
+        android:layout_marginTop="3dp"
+        android:layout_marginEnd="6dp"
+        android:text="Summary"
+        android:textAppearance="@style/TextAppearance.AppCompat.Medium"
+        android:textColor="?android:attr/textColorPrimary"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/vSeparatorCalendar" />
+
+    <TextView
+        android:id="@+id/tvCalendarStart"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:layout_marginStart="6dp"
+        android:layout_marginTop="6dp"
+        android:layout_marginEnd="6dp"
+        android:text="12:00:00"
+        android:textAppearance="@style/TextAppearance.AppCompat.Small"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/tvCalendarSummary" />
+
+    <TextView
+        android:id="@+id/tvCalendarEnd"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:layout_marginStart="6dp"
+        android:layout_marginTop="3dp"
+        android:layout_marginEnd="6dp"
+        android:text="12:00:00"
+        android:textAppearance="@style/TextAppearance.AppCompat.Small"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/tvCalendarStart" />
+
+    <TextView
+        android:id="@+id/tvAttendees"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:layout_marginStart="6dp"
+        android:layout_marginTop="6dp"
+        android:layout_marginEnd="6dp"
+        android:text="You, me"
+        android:textAppearance="@style/TextAppearance.AppCompat.Small"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/tvCalendarEnd" />
+
+    <View
+        android:id="@+id/paddingBottom"
+        android:layout_width="wrap_content"
+        android:layout_height="6dp"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/tvAttendees" />
+
+    <eu.faircode.email.ContentLoadingProgressBar
+        android:id="@+id/pbCalendarWait"
+        style="@style/Base.Widget.AppCompat.ProgressBar"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_margin="12dp"
+        android:indeterminate="true"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent" />
+
+    <androidx.constraintlayout.widget.Group
+        android:id="@+id/grpCalendar"
+        android:layout_width="0dp"
+        android:layout_height="0dp"
+        app:constraint_referenced_ids="vSeparatorCalendar,paddingBottom" />
+</androidx.constraintlayout.widget.ConstraintLayout>
\ No newline at end of file
diff --git a/app/src/main/res/layout/item_message_compact.xml b/app/src/main/res/layout/item_message_compact.xml
index 12d2276cd9..2023abcecf 100644
--- a/app/src/main/res/layout/item_message_compact.xml
+++ b/app/src/main/res/layout/item_message_compact.xml
@@ -350,13 +350,21 @@
             app:layout_constraintStart_toStartOf="parent"
             app:layout_constraintTop_toBottomOf="@id/inMessage" />
 
+        <include
+            android:id="@+id/InCalendar"
+            layout="@layout/include_message_calendar"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toBottomOf="@id/vwBody" />
+
         <include
             android:id="@+id/inAttachmentsAlt"
             layout="@layout/include_message_attachments"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             app:layout_constraintStart_toStartOf="parent"
-            app:layout_constraintTop_toBottomOf="@id/vwBody" />
+            app:layout_constraintTop_toBottomOf="@id/InCalendar" />
 
         <include
             android:id="@+id/inImages"
diff --git a/app/src/main/res/layout/item_message_normal.xml b/app/src/main/res/layout/item_message_normal.xml
index 89a90fe47c..3d3760bbb6 100644
--- a/app/src/main/res/layout/item_message_normal.xml
+++ b/app/src/main/res/layout/item_message_normal.xml
@@ -343,13 +343,21 @@
             app:layout_constraintStart_toStartOf="parent"
             app:layout_constraintTop_toBottomOf="@id/inMessage" />
 
+        <include
+            android:id="@+id/InCalendar"
+            layout="@layout/include_message_calendar"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toBottomOf="@id/vwBody" />
+
         <include
             android:id="@+id/inAttachmentsAlt"
             layout="@layout/include_message_attachments"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             app:layout_constraintStart_toStartOf="parent"
-            app:layout_constraintTop_toBottomOf="@id/vwBody" />
+            app:layout_constraintTop_toBottomOf="@id/InCalendar" />
 
         <include
             android:id="@+id/inImages"
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index c2e6d9c88d..b0d5ade7a9 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -682,6 +682,10 @@
     <string name="title_no_charset">Unsupported encoding: %1$s</string>
     <string name="title_via">Via: %1$s</string>
 
+    <string name="title_icalendar_accept">Accept</string>
+    <string name="title_icalendar_decline">Decline</string>
+    <string name="title_icalendar_maybe">Maybe</string>
+
     <string name="title_try">Try FairEmail, an open source, privacy friendly email app for Android</string>
 
     <string name="title_pro_feature">This is a pro feature</string>