Thank you for your post.
Error 1503 is an error with SSL. Assuming this is a SSL issue, can you try accessing the SMTP server without SSL or authentication? Or, can you temporarily set up the SMTP server without SSL? I cannot test this as I do not have access to a SMTP server from my iOS devices (the SMTP server is within the firewall, and my iOS devices are not).
What occurs if you use the E-Mail Client setting?
Any other information you can provide may be helpful as I pass this information along to Testing and Development.