Dealing with Dependencies in Active Record Models — Option #2: Using a new object

Invitation.php

<?php

class Invitation extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class, 'invited_by');
    }
}

InvitationsController.php

<?php

class InvitationsController extends Controller
{
    private $invitationSender;

    public function __construct(InvitationSender $invitationSender)
    {
        $this->invitationSender = $invitationSender;
    }

    public function store()
    {
        $invitation = Invitation::create([
            'recipient' => request('recipient'),
            'invited_by' => auth()->user()->id,
        ]);

        $this->invitationSender->send($invitation);

        return response('', 204);
    }
}

InvitationSender.php

<?php

class InvitationSender
{
    private $mailer;

    public function __construct(Mailer $mailer)
    {
        $this->mailer = $mailer;
    }

    public function send($invitation)
    {
        $this->mailer->send('emails.invitation', ['invited_by' => $invitation->user], function ($m) use ($invitation) {
            $m->to($invitation->recipient)->subject("You've been invited to my app!");
        });
    }
}