I've discovered an issue with a production system I'm administrating/building.
Clients via web direct fill out a form and once confirmed activates a PSOS which creates a PDF summary and emails it to them. If the client has a "." in the first part of their email address the system barks out an error stating "The email(s) could not be sent" - this only happens for emails with a "." before the @ symbol example "email@example.com"
If I send an email to the same address via the same SMTP server using a client it works fine so it appear to be a issue specific to Filemaker.
Hoping it's a quick fix..