In this video it shows the steps to read the Gmail’s inbox programmatically in your Android App. It uses Java libraries to implement this.

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Complete source code and other details:

package com.programmerworld.gmailinboxapp;

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.os.StrictMode;
import android.view.View;
import android.widget.TextView;

import java.io.IOException;
import java.util.Properties;

import javax.mail.Folder;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Multipart;
import javax.mail.NoSuchProviderException;
import javax.mail.Session;
import javax.mail.Store;

public class MainActivity extends AppCompatActivity {
    private TextView textView;
    private String stringMailHost = "imap.gmail.com";
    private Session session;
    private Store store;
    private Properties properties;
    private String stringUserName = "receiveremail963";
    private  String stringPassword = "miutwafelszamolh";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = findViewById(R.id.textView);
        StrictMode.ThreadPolicy threadPolicy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
        StrictMode.setThreadPolicy(threadPolicy);
        properties = System.getProperties();
        if (properties == null){
            textView.setText("Properties is NULL");
            return;
        }
        else {
            properties.setProperty("mail.store.protocol", "imaps");
        }
        try {
            session = Session.getDefaultInstance(properties, null);
            store = session.getStore("imaps");
            store.connect(stringMailHost, stringUserName, stringPassword);
            textView.setText("Connection successful");
        } catch (NoSuchProviderException e) {
            throw new RuntimeException(e);
        } catch (MessagingException e) {
            throw new RuntimeException(e);
        }
    }
    public void buttonReadGmail(View view){
        readGmail();
    }
    public synchronized void readGmail(){
        try {
            Folder folder = store.getFolder("Inbox");
            folder.open(Folder.READ_ONLY);
            Message[] messages = folder.getMessages();
            textView.setText("Total Messages = " + messages.length + "\n\n" +
                    messages[9].getFrom()[0].toString() + "\n\n" +
                    messages[9].getSubject() + "\n\n" +
                    ((Multipart)messages[9].getContent()).getBodyPart(0).getContent().toString());

        } catch (MessagingException e) {
            throw new RuntimeException(e);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">

    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.GmailInboxApp"
        tools:targetApi="31">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

plugins {
    id("com.android.application")
}

android {
    namespace = "com.programmerworld.gmailinboxapp"
    compileSdk = 34

    defaultConfig {
        applicationId = "com.programmerworld.gmailinboxapp"
        minSdk = 34
        targetSdk = 34
        versionCode = 1
        versionName = "1.0"

        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            isMinifyEnabled = false
            proguardFiles(
                getDefaultProguardFile("proguard-android-optimize.txt"),
                "proguard-rules.pro"
            )
        }
    }
    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_1_8
        targetCompatibility = JavaVersion.VERSION_1_8
    }

    packaging{
        resources.excludes.add("META-INF/NOTICE.md")
        resources.excludes.add("META-INF/LICENSE.md")
    }

}

dependencies {

    implementation("androidx.appcompat:appcompat:1.6.1")
    implementation("com.google.android.material:material:1.10.0")
    implementation("androidx.constraintlayout:constraintlayout:2.1.4")
    testImplementation("junit:junit:4.13.2")
    androidTestImplementation("androidx.test.ext:junit:1.1.5")
    androidTestImplementation("androidx.test.espresso:espresso-core:3.5.1")

    implementation("com.sun.mail:android-mail:1.6.6")
    implementation("com.sun.mail:android-activation:1.6.7")

}

<?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="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="145dp"
        android:layout_marginTop="61dp"
        android:onClick="buttonReadGmail"
        android:text="Read Gmail"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

Screenshots: