For anyone stumbling across this in the future still looking for an answer, a support rep replied to my ticket and suggested this is a known issue with SP17 on 6.5. Ref: CQ-4353652 Good luck all!

Setting the log level to debug does not appear to generate any additional log output information. Wondering if I'm missing something in the configuration there... but otherwise nothing sticks out? Same error as in the original post is present, nothing more. As for SMTP access

Not on AEMaaCS, this is AMS/ACM. Regardless, going to see about accessing to grab the error.log.

Will see about grabbing the full error.log. ...validate : That the AEM instance can successfully connect to the configured SMTP server. Yes, this instance is able to access the smtp server.Confirm that the submitting user and assigned group have valid email addresses associated with their user accou...

The old tried and true. This was the first thing we tried though!

Well, that's the thing... This is all that is being posted in the log. 

Hello all! The community has been very helpful with past issues, so I figured I'd bring this one here as well - Perhaps you'll all have some ideas. I've seen a lot of people with EMailNotificationService or various other workflow-email-related issues that are typically configuration errors resolved ...

Thank you for the documentation. I believe I've got everything working at this point. Going to attempt to go through our 4 or so custom components (using images) and get them up to speed as well. Thank you again for all your help here.

Please see my design dialog code snippet above - it is near identical to the Image V3 core component (I just adjusted the accepted MIME types). I misunderstood. I'll try adding this now! Could you expand on this second part? I'm referencing the core component model directly at the moment, but my und...

It is a new component, not inheriting.