diff --git a/mail/common/build.gradle b/mail/common/build.gradle
index f445e3e27..5ce857634 100644
--- a/mail/common/build.gradle
+++ b/mail/common/build.gradle
@@ -10,7 +10,6 @@ dependencies {
     implementation "org.apache.james:apache-mime4j-dom:${versions.mime4j}"
     implementation "com.squareup.okio:okio:${versions.okio}"
     implementation "commons-io:commons-io:${versions.commonsIo}"
-    implementation "androidx.annotation:annotation:${versions.androidxAnnotation}"
     implementation "com.jakewharton.timber:timber:${versions.timber}"
 
     testImplementation project(":mail:testing")
diff --git a/mail/common/src/main/java/com/fsck/k9/mail/Address.java b/mail/common/src/main/java/com/fsck/k9/mail/Address.java
index d90aa220a..587ce7a26 100644
--- a/mail/common/src/main/java/com/fsck/k9/mail/Address.java
+++ b/mail/common/src/main/java/com/fsck/k9/mail/Address.java
@@ -1,8 +1,6 @@
 
 package com.fsck.k9.mail;
 
-import androidx.annotation.NonNull;
-import androidx.annotation.VisibleForTesting;
 
 import java.io.Serializable;
 import java.util.ArrayList;
@@ -15,6 +13,8 @@ import org.apache.james.mime4j.codec.EncoderUtil;
 import org.apache.james.mime4j.dom.address.Mailbox;
 import org.apache.james.mime4j.dom.address.MailboxList;
 import org.apache.james.mime4j.field.address.DefaultAddressParser;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.VisibleForTesting;
 import timber.log.Timber;
 
 import android.text.TextUtils;
@@ -29,7 +29,7 @@ public class Address implements Serializable {
      */
     private static final Address[] EMPTY_ADDRESS_ARRAY = new Address[0];
 
-    @NonNull
+    @NotNull
     private String mAddress;
 
     private String mPersonal;
diff --git a/mail/common/src/main/java/com/fsck/k9/mail/BoundaryGenerator.java b/mail/common/src/main/java/com/fsck/k9/mail/BoundaryGenerator.java
index 9b2452e61..87c463273 100644
--- a/mail/common/src/main/java/com/fsck/k9/mail/BoundaryGenerator.java
+++ b/mail/common/src/main/java/com/fsck/k9/mail/BoundaryGenerator.java
@@ -3,7 +3,7 @@ package com.fsck.k9.mail;
 
 import java.util.Random;
 
-import androidx.annotation.VisibleForTesting;
+import org.jetbrains.annotations.VisibleForTesting;
 
 
 public class BoundaryGenerator {
diff --git a/mail/common/src/main/java/com/fsck/k9/mail/Message.java b/mail/common/src/main/java/com/fsck/k9/mail/Message.java
index c7aa729fd..91e3a8043 100644
--- a/mail/common/src/main/java/com/fsck/k9/mail/Message.java
+++ b/mail/common/src/main/java/com/fsck/k9/mail/Message.java
@@ -8,10 +8,9 @@ import java.util.EnumSet;
 import java.util.List;
 import java.util.Set;
 
-import androidx.annotation.NonNull;
-
 import com.fsck.k9.mail.filter.CountingOutputStream;
 import com.fsck.k9.mail.filter.EOLConvertingOutputStream;
+import org.jetbrains.annotations.NotNull;
 import timber.log.Timber;
 
 
@@ -98,7 +97,7 @@ public abstract class Message implements Part, Body {
     @Override
     public abstract void setHeader(String name, String value);
 
-    @NonNull
+    @NotNull
     @Override
     public abstract String[] getHeader(String name);
 
diff --git a/mail/common/src/main/java/com/fsck/k9/mail/Part.java b/mail/common/src/main/java/com/fsck/k9/mail/Part.java
index c3fb55e7c..655c3bb5c 100644
--- a/mail/common/src/main/java/com/fsck/k9/mail/Part.java
+++ b/mail/common/src/main/java/com/fsck/k9/mail/Part.java
@@ -4,7 +4,7 @@ package com.fsck.k9.mail;
 import java.io.IOException;
 import java.io.OutputStream;
 
-import androidx.annotation.NonNull;
+import org.jetbrains.annotations.NotNull;
 
 
 public interface Part {
@@ -27,7 +27,7 @@ public interface Part {
     /**
      * Returns an array of headers of the given name. The array may be empty.
      */
-    @NonNull
+    @NotNull
     String[] getHeader(String name);
 
     boolean isMimeType(String mimeType);
diff --git a/mail/common/src/main/java/com/fsck/k9/mail/internet/MessageExtractor.java b/mail/common/src/main/java/com/fsck/k9/mail/internet/MessageExtractor.java
index c54f469be..c66d73c2c 100644
--- a/mail/common/src/main/java/com/fsck/k9/mail/internet/MessageExtractor.java
+++ b/mail/common/src/main/java/com/fsck/k9/mail/internet/MessageExtractor.java
@@ -10,9 +10,6 @@ import java.util.Set;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
-import androidx.annotation.NonNull;
-import androidx.annotation.Nullable;
-
 import com.fsck.k9.mail.Body;
 import com.fsck.k9.mail.BodyPart;
 import com.fsck.k9.mail.Message;
@@ -20,6 +17,8 @@ import com.fsck.k9.mail.MessagingException;
 import com.fsck.k9.mail.Multipart;
 import com.fsck.k9.mail.Part;
 import org.apache.commons.io.input.BoundedInputStream;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 import timber.log.Timber;
 
 import static com.fsck.k9.mail.internet.CharsetSupport.fixupCharset;
@@ -407,7 +406,7 @@ public class MessageExtractor {
      *         A list that will receive the parts that are considered attachments.
      */
     private static void findAttachments(Multipart multipart, Set<Part> knownTextParts,
-            @NonNull List<Part> attachments) {
+            @NotNull List<Part> attachments) {
         for (Part part : multipart.getBodyParts()) {
             Body body = part.getBody();
             if (body instanceof Multipart) {
diff --git a/mail/common/src/main/java/com/fsck/k9/mail/internet/MimeBodyPart.java b/mail/common/src/main/java/com/fsck/k9/mail/internet/MimeBodyPart.java
index 1c86dec2d..591f8230d 100644
--- a/mail/common/src/main/java/com/fsck/k9/mail/internet/MimeBodyPart.java
+++ b/mail/common/src/main/java/com/fsck/k9/mail/internet/MimeBodyPart.java
@@ -12,8 +12,6 @@ import java.io.IOException;
 import java.io.OutputStream;
 import java.io.OutputStreamWriter;
 
-import androidx.annotation.NonNull;
-
 import org.jetbrains.annotations.NotNull;
 
 import static com.fsck.k9.mail.internet.MimeUtility.isSameMimeType;
@@ -86,7 +84,7 @@ public class MimeBodyPart extends BodyPart {
         mHeader.setHeader(name, value);
     }
 
-    @NonNull
+    @NotNull
     @Override
     public String[] getHeader(String name) {
         return mHeader.getHeader(name);
diff --git a/mail/common/src/main/java/com/fsck/k9/mail/internet/MimeMessage.java b/mail/common/src/main/java/com/fsck/k9/mail/internet/MimeMessage.java
index 81d823694..6ec9b65db 100644
--- a/mail/common/src/main/java/com/fsck/k9/mail/internet/MimeMessage.java
+++ b/mail/common/src/main/java/com/fsck/k9/mail/internet/MimeMessage.java
@@ -15,8 +15,6 @@ import java.util.List;
 import java.util.Locale;
 import java.util.TimeZone;
 
-import androidx.annotation.NonNull;
-
 import com.fsck.k9.mail.Address;
 import com.fsck.k9.mail.Body;
 import com.fsck.k9.mail.BodyFactory;
@@ -38,6 +36,7 @@ import org.apache.james.mime4j.parser.MimeStreamParser;
 import org.apache.james.mime4j.stream.BodyDescriptor;
 import org.apache.james.mime4j.stream.Field;
 import org.apache.james.mime4j.stream.MimeConfig;
+import org.jetbrains.annotations.NotNull;
 import timber.log.Timber;
 
 
@@ -434,7 +433,7 @@ public class MimeMessage extends Message {
         mHeader.setHeader(name, value);
     }
 
-    @NonNull
+    @NotNull
     @Override
     public String[] getHeader(String name) {
         return mHeader.getHeader(name);
diff --git a/mail/common/src/main/java/com/fsck/k9/mail/internet/MimeUtility.java b/mail/common/src/main/java/com/fsck/k9/mail/internet/MimeUtility.java
index c9b61ccd1..1991c33a5 100644
--- a/mail/common/src/main/java/com/fsck/k9/mail/internet/MimeUtility.java
+++ b/mail/common/src/main/java/com/fsck/k9/mail/internet/MimeUtility.java
@@ -9,9 +9,6 @@ import java.util.Locale;
 import java.util.Map;
 import java.util.regex.Pattern;
 
-import androidx.annotation.NonNull;
-import androidx.annotation.VisibleForTesting;
-
 import com.fsck.k9.mail.Body;
 import com.fsck.k9.mail.BodyPart;
 import com.fsck.k9.mail.Message;
@@ -21,6 +18,8 @@ import com.fsck.k9.mail.Part;
 import org.apache.james.mime4j.codec.Base64InputStream;
 import org.apache.james.mime4j.codec.QuotedPrintableInputStream;
 import org.apache.james.mime4j.util.MimeUtil;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.VisibleForTesting;
 import timber.log.Timber;
 
 
@@ -1069,7 +1068,7 @@ public class MimeUtility {
         return DEFAULT_ATTACHMENT_MIME_TYPE;
     }
 
-    public static String getExtensionByMimeType(@NonNull String mimeType) {
+    public static String getExtensionByMimeType(@NotNull String mimeType) {
         String lowerCaseMimeType = mimeType.toLowerCase(Locale.US);
         for (String[] contentTypeMapEntry : MIME_TYPE_BY_EXTENSION_MAP) {
             if (contentTypeMapEntry[1].equals(lowerCaseMimeType)) {
diff --git a/mail/common/src/main/java/com/fsck/k9/mail/internet/TextBody.java b/mail/common/src/main/java/com/fsck/k9/mail/internet/TextBody.java
index 414be33d2..6a5902a11 100644
--- a/mail/common/src/main/java/com/fsck/k9/mail/internet/TextBody.java
+++ b/mail/common/src/main/java/com/fsck/k9/mail/internet/TextBody.java
@@ -7,8 +7,6 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 
-import androidx.annotation.Nullable;
-
 import com.fsck.k9.mail.Body;
 import com.fsck.k9.mail.MessagingException;
 import com.fsck.k9.mail.filter.CountingOutputStream;
@@ -17,6 +15,7 @@ import com.fsck.k9.mail.filter.SignSafeOutputStream;
 import org.apache.james.mime4j.Charsets;
 import org.apache.james.mime4j.codec.QuotedPrintableOutputStream;
 import org.apache.james.mime4j.util.MimeUtil;
+import org.jetbrains.annotations.Nullable;
 
 
 public class TextBody implements Body, SizeAware {
diff --git a/mail/protocols/imap/build.gradle b/mail/protocols/imap/build.gradle
index 54e9e80df..494445041 100644
--- a/mail/protocols/imap/build.gradle
+++ b/mail/protocols/imap/build.gradle
@@ -12,7 +12,6 @@ dependencies {
     implementation "com.beetstra.jutf7:jutf7:1.0.0"
     implementation "commons-io:commons-io:${versions.commonsIo}"
     implementation "com.jakewharton.timber:timber:${versions.timber}"
-    implementation "androidx.annotation:annotation:${versions.androidxAnnotation}"
 
     testImplementation project(":mail:testing")
     testImplementation "org.robolectric:robolectric:${versions.robolectric}"
diff --git a/mail/protocols/imap/src/main/java/com/fsck/k9/mail/store/imap/ListResponse.java b/mail/protocols/imap/src/main/java/com/fsck/k9/mail/store/imap/ListResponse.java
index 4ae0d9dea..57e38f73e 100644
--- a/mail/protocols/imap/src/main/java/com/fsck/k9/mail/store/imap/ListResponse.java
+++ b/mail/protocols/imap/src/main/java/com/fsck/k9/mail/store/imap/ListResponse.java
@@ -5,7 +5,7 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
-import androidx.annotation.Nullable;
+import org.jetbrains.annotations.Nullable;
 
 import static com.fsck.k9.mail.store.imap.ImapResponseParser.equalsIgnoreCase;
 
diff --git a/mail/protocols/imap/src/main/java/com/fsck/k9/mail/store/imap/RealImapStore.java b/mail/protocols/imap/src/main/java/com/fsck/k9/mail/store/imap/RealImapStore.java
index 3011442f7..1f89e0ce9 100644
--- a/mail/protocols/imap/src/main/java/com/fsck/k9/mail/store/imap/RealImapStore.java
+++ b/mail/protocols/imap/src/main/java/com/fsck/k9/mail/store/imap/RealImapStore.java
@@ -13,8 +13,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
-import androidx.annotation.Nullable;
-
 import com.fsck.k9.mail.AuthType;
 import com.fsck.k9.mail.ConnectionSecurity;
 import com.fsck.k9.mail.Flag;
@@ -24,6 +22,7 @@ import com.fsck.k9.mail.ServerSettings;
 import com.fsck.k9.mail.oauth.OAuth2TokenProvider;
 import com.fsck.k9.mail.ssl.TrustedSocketFactory;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 import timber.log.Timber;
 
 
diff --git a/mail/protocols/pop3/build.gradle b/mail/protocols/pop3/build.gradle
index f7afb0a6a..a99cfe4f0 100644
--- a/mail/protocols/pop3/build.gradle
+++ b/mail/protocols/pop3/build.gradle
@@ -8,7 +8,6 @@ dependencies {
     api project(":mail:common")
 
     implementation "com.jakewharton.timber:timber:${versions.timber}"
-    implementation "androidx.annotation:annotation:${versions.androidxAnnotation}"
 
     testImplementation project(":mail:testing")
     testImplementation "org.robolectric:robolectric:${versions.robolectric}"
diff --git a/mail/protocols/pop3/src/main/java/com/fsck/k9/mail/store/pop3/Pop3Store.java b/mail/protocols/pop3/src/main/java/com/fsck/k9/mail/store/pop3/Pop3Store.java
index cba76ff04..4542caaed 100644
--- a/mail/protocols/pop3/src/main/java/com/fsck/k9/mail/store/pop3/Pop3Store.java
+++ b/mail/protocols/pop3/src/main/java/com/fsck/k9/mail/store/pop3/Pop3Store.java
@@ -4,13 +4,12 @@ package com.fsck.k9.mail.store.pop3;
 import java.util.HashMap;
 import java.util.Map;
 
-import androidx.annotation.NonNull;
-
 import com.fsck.k9.mail.AuthType;
 import com.fsck.k9.mail.ConnectionSecurity;
 import com.fsck.k9.mail.MessagingException;
 import com.fsck.k9.mail.ServerSettings;
 import com.fsck.k9.mail.ssl.TrustedSocketFactory;
+import org.jetbrains.annotations.NotNull;
 
 
 public class Pop3Store {
@@ -36,7 +35,7 @@ public class Pop3Store {
         authType = serverSettings.authenticationType;
     }
 
-    @NonNull
+    @NotNull
     public Pop3Folder getFolder(String name) {
         Pop3Folder folder = mFolders.get(name);
         if (folder == null) {
diff --git a/mail/protocols/smtp/build.gradle b/mail/protocols/smtp/build.gradle
index 478cd591b..8ec2ecb1d 100644
--- a/mail/protocols/smtp/build.gradle
+++ b/mail/protocols/smtp/build.gradle
@@ -11,7 +11,6 @@ dependencies {
     implementation "commons-io:commons-io:${versions.commonsIo}"
     implementation "com.squareup.okio:okio:${versions.okio}"
     implementation "com.jakewharton.timber:timber:${versions.timber}"
-    implementation "androidx.annotation:annotation:${versions.androidxAnnotation}"
 
     testImplementation project(":mail:testing")
     testImplementation "org.robolectric:robolectric:${versions.robolectric}"
diff --git a/mail/protocols/webdav/build.gradle b/mail/protocols/webdav/build.gradle
index 59634c5a6..a14c8083c 100644
--- a/mail/protocols/webdav/build.gradle
+++ b/mail/protocols/webdav/build.gradle
@@ -9,7 +9,6 @@ dependencies {
 
     implementation "commons-io:commons-io:${versions.commonsIo}"
     implementation "com.jakewharton.timber:timber:${versions.timber}"
-    implementation "androidx.annotation:annotation:${versions.androidxAnnotation}"
 
     testImplementation project(":mail:testing")
     testImplementation "org.robolectric:robolectric:${versions.robolectric}"