A great feature would be if an email fails to send then it sends an email alert to the admin. It could use the fallback connection or use default PHP mail if no fallback is configured.
Using a fallback connection is great, but I have no one of knowing the fallback connection is getting used unless I manually monitor the email logs.
Or it could even send the email alert via default PHP mail.
Probably limiting the alert to once a day would be good in case of lots of failed emails occurring.