As of the last few days, emails that are sent via mobile devices that HAVE attachments will not send. They just sit in the OUTBOX. It doesn't matter what size attachment it is. 1k, 3MB, etc. Outlook clients are fine on desktops and laptops, no issues. (mix of Outlook 2016 & 2010) Running Exchange 2010 All the certs are fine on the hub transport servers, nothing has been changed nor expired.
No recent server updates
restarted the servers, IIS. If you send an email with an android or apple with no attachment it's fine.