my Controller

<?php

namespace App\Http\Controllers;

use App\Task;
use Illuminate\Http\Request;
use Illuminate\Support\Facades\Validator;
use Twilio\Rest\Client;
use App\Notifications\CustomEmail;
use Mail;
use App\Mail\ContactMail;

class EmailController extends Controller
{
    /**
     * Display a listing of the resource.
     *
     * @return \Illuminate\Http\Response
     */
    public function index()
    {
        $tasks = Task::paginate(15);
        return view('send.mail',compact('tasks',$tasks));
    }

    public function sendmail(Request $get)
    {
        $validatedData = $get->validate([
            'tasks' => 'required|array',
            "subject" => "required",
            "message" => "required",
        ]);
    
        $tasks = $validatedData["tasks"];
        
        foreach ($tasks as $task) {
            $mail = ($task->mail);
            $subject = $get->subject;
            $message = $get->message;

            Mail::to($mail)->send(new ContactMail($subject, $message) );
    }
        
    }
}

ContactMail.php

<?php

namespace App\Mail;

use Illuminate\Bus\Queueable;
use Illuminate\Http\Request;
use Illuminate\Mail\Mailable;
use Illuminate\Queue\SerializesModels;
use Illuminate\Contracts\Queue\ShouldQueue;

class ContactMail extends Mailable
{
    use Queueable, SerializesModels;

    public $sub;
    public $mes;

    /**
     * Create a new message instance.
     *
     * @return void
     */
    public function __construct($subject, $message)
    {
        $this->sub = $subject;
        $this->mes = $message;
    }

    /**
     * Build the message.
     *
     * @return $this
     */
    public function build()
    {
        $e_subject = $this->sub;
        $e_message = $this->mes;

        return $this->view('email.contactmail', compact("e_message"))->subject("$e_subject");
    }
}

Form

@extends('layouts.index')

@section('content')
            @if (session('success'))
            <div class="alert alert-success">
                {{ session('success') }}
            </div>
            @endif
            @if ($errors->any())
            <div class="alert alert-danger">
                <ul>
                    @foreach ($errors->all() as $error)
                    <li>{{ $error }}</li>
                    @endforeach
                </ul>
            </div>
            @endif
                <div class="col">
                    <div class="card">
                        <div class="card-body">
                            <form method="POST" action="{{url('send/email')}}">
                                @csrf
                                <label><h3>Notify Contractors via EMail</h3></label>
                                <div class="form-group">
                                {{Form::label('subject', 'Subject')}}
                                    {{Form::text('subject', '', ['class' => 'form-control', 'placeholder' => 'Subject'])}}
                                </div>
                                <div class="form-group">
                                <label>Select Address</label>
                                    <select name="tasks[]" multiple class="form-control" >
                                        @foreach ($tasks as $task)
                                        <option>{{$task->mail}}</option>
                                        @endforeach
                                    </select>
                                </div>
                                <div class="form-group">
                                    <label>Message</label>
                                    <textarea name="message" type="text" class="form-control" rows="3"></textarea>
                                </div>
                                <button type="submit" class="btn btn-primary">Send Notification</button>
                            </form>
                        </div>
                    </div>
                </div>

@endsection