simple-email/app/src/main/res/layout/fragment_compose.xml

<?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"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ScrollView xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@+id/bottom_navigation"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <androidx.constraintlayout.widget.ConstraintLayout xmlns:app="http://schemas.android.com/apk/res-auto"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <Spinner
                android:id="@+id/spFrom"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginTop="6dp"
                app:layout_constraintEnd_toStartOf="@+id/ivIdentityAdd"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent" />

            <ImageView
                android:id="@+id/ivIdentityAdd"
                android:layout_width="24dp"
                android:layout_height="24dp"
                android:layout_marginStart="6dp"
                android:layout_marginEnd="6dp"
                android:src="@drawable/baseline_person_add_24"
                app:layout_constraintBottom_toBottomOf="@id/spFrom"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintTop_toTopOf="@id/spFrom" />

            <MultiAutoCompleteTextView
                android:id="@+id/etTo"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginStart="6dp"
                android:hint="@string/title_to"
                android:inputType="textEmailAddress|textMultiLine"
                android:singleLine="true"
                android:textAppearance="@style/TextAppearance.AppCompat.Medium"
                app:layout_constraintEnd_toStartOf="@+id/ivToAdd"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/spFrom" />

            <ImageView
                android:id="@+id/ivToAdd"
                android:layout_width="24dp"
                android:layout_height="24dp"
                android:layout_marginStart="6dp"
                android:layout_marginEnd="6dp"
                android:src="@drawable/baseline_person_24"
                app:layout_constraintBottom_toBottomOf="@id/etTo"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toEndOf="@id/etTo"
                app:layout_constraintTop_toTopOf="@+id/etTo" />

            <MultiAutoCompleteTextView
                android:id="@+id/etCc"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginStart="6dp"
                android:hint="@string/title_cc"
                android:inputType="textEmailAddress|textMultiLine"
                android:singleLine="true"
                android:textAppearance="@style/TextAppearance.AppCompat.Medium"
                app:layout_constraintEnd_toStartOf="@+id/ivCcAdd"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/etTo" />

            <ImageView
                android:id="@+id/ivCcAdd"
                android:layout_width="24dp"
                android:layout_height="24dp"
                android:layout_marginStart="6dp"
                android:layout_marginEnd="6dp"
                android:src="@drawable/baseline_person_24"
                app:layout_constraintBottom_toBottomOf="@id/etCc"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toEndOf="@id/etCc"
                app:layout_constraintTop_toTopOf="@+id/etCc" />

            <MultiAutoCompleteTextView
                android:id="@+id/etBcc"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginStart="6dp"
                android:hint="@string/title_bcc"
                android:inputType="textEmailAddress|textMultiLine"
                android:singleLine="true"
                android:textAppearance="@style/TextAppearance.AppCompat.Medium"
                app:layout_constraintEnd_toStartOf="@+id/ivBccAdd"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/etCc" />

            <ImageView
                android:id="@+id/ivBccAdd"
                android:layout_width="24dp"
                android:layout_height="24dp"
                android:layout_marginStart="6dp"
                android:layout_marginEnd="6dp"
                android:src="@drawable/baseline_person_24"
                app:layout_constraintBottom_toBottomOf="@id/etBcc"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toEndOf="@id/etBcc"
                app:layout_constraintTop_toTopOf="@+id/etBcc" />

            <EditText
                android:id="@+id/etSubject"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginStart="6dp"
                android:layout_marginEnd="6dp"
                android:hint="@string/title_subject"
                android:inputType="textEmailSubject|textCapSentences|textMultiLine"
                android:singleLine="true"
                android:textAppearance="@style/TextAppearance.AppCompat.Medium"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/etBcc" />

            <View
                android:id="@+id/vSeparatorAttachments"
                android:layout_width="match_parent"
                android:layout_height="1dp"
                android:layout_marginTop="3dp"
                android:background="?attr/colorSeparator"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@id/etSubject" />

            <androidx.recyclerview.widget.RecyclerView
                android:id="@+id/rvAttachment"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginStart="6dp"
                android:layout_marginTop="3dp"
                android:layout_marginEnd="6dp"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/vSeparatorAttachments" />

            <View
                android:id="@+id/vSeparator"
                android:layout_width="match_parent"
                android:layout_height="1dp"
                android:layout_marginTop="6dp"
                android:background="?attr/colorSeparator"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/rvAttachment" />

            <EditText
                android:id="@+id/etBody"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginStart="6dp"
                android:layout_marginEnd="6dp"
                android:background="@null"
                android:fontFamily="monospace"
                android:gravity="top"
                android:hint="@string/title_body_hint"
                android:inputType="textCapSentences|textMultiLine"
                android:minHeight="480dp"
                android:textAppearance="@style/TextAppearance.AppCompat.Small"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@id/vSeparator" />

            <androidx.constraintlayout.widget.Group
                android:id="@+id/grpHeader"
                android:layout_width="0dp"
                android:layout_height="0dp"
                app:constraint_referenced_ids="spFrom,ivIdentityAdd,etTo,ivToAdd,etSubject,vSeparator" />

            <androidx.constraintlayout.widget.Group
                android:id="@+id/grpAddresses"
                android:layout_width="0dp"
                android:layout_height="0dp"
                app:constraint_referenced_ids="etCc,ivCcAdd,etBcc,ivBccAdd" />

            <androidx.constraintlayout.widget.Group
                android:id="@+id/grpAttachments"
                android:layout_width="0dp"
                android:layout_height="0dp"
                app:constraint_referenced_ids="vSeparatorAttachments,rvAttachment" />
        </androidx.constraintlayout.widget.ConstraintLayout>
    </ScrollView>

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottom_navigation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/colorPrimary"
        app:itemIconTint="@color/bottomnav_background"
        app:itemTextColor="@color/bottomnav_background"
        app:labelVisibilityMode="labeled"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:menu="@menu/action_compose" />

    <ProgressBar
        android:id="@+id/pbWait"
        style="@style/Base.Widget.AppCompat.ProgressBar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        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.ConstraintLayout>