Queued emails are (intermittently) not sent, but jobs are completing successfully.

I have queued emails which work... some of the time. After a few hours, the queued jobs are created, processed and marked as done, but there is no communication with the smtp server (microsoft exchange).

Some relevant code is below:

In the controller:

      // $bcc =  list of addresses
      Mail::to('[email protected]')->bcc($bcc)->send(new NewPatientNotification("test", "email.newpatient"));

The mailable

class NewPatientNotification extends Mailable implements ShouldQueue
{
  use Queueable, SerializesModels;

  public function __construct(public string $subj, public string $viewName)
  {
    log_info("New Patient Notification Construct: sending email for ....");
  }

  public function build()
  {
    log_info("New Patient Notification Build");
    return $this->subject($this->subj)->view($this->viewName);
  }
}

The log (this one worked):

  2025-03-20 07:14:00 App\Mail\NewPatientNotification ................ RUNNING
  LOG: [user_id=0]App\Mail\NewPatientNotification@build(36): New Patient Notification Build:
  2025-03-20 07:14:02 App\Mail\NewPatientNotification ................ 2s DONE

The log (this one didn't work):

  2025-04-03 15:08:34 App\Mail\NewPatientNotification ................ RUNNING
  LOG: [user_id=0]App\Mail\NewPatientNotification@build(36): New Patient Notification Build:
  2025-04-03 15:08:34 App\Mail\NewPatientNotification ........... 56.17ms DONE

The only thing I noticed is the emails that are sent tend to take 500ms or more. The ones that don't send tend to be 100ms or less.