Last tested: Sep 19, 2019
1) The message failed to be delivered to the SMTP server
There have been a couple incidents in the past where using the "pretty" email domain
User Name <email@example.com> instead of simply `firstname.lastname@example.org` has caused the "Test" button to work in the SMTP test page, but caused various SMTP errors when actually sending content
The admin should try using just
2) The relay server or receiver of the email is blocking the email from going through
There are some situations where the SMTP server itself or spam filters will block certain emails differently, so even though the test email may have gone through, the scheduled email with attachments and a different email body could be causing issues.
In this case, you would need to look at your SMTP server's logs to see if the email got to the SMTP server, and if so if it was blocked/bounced or sent on to the email to the recipient.