Thanks Stefano – that helped. I was able to chat with the support and essentially get my SMTP configuration right. Apparently, it wasn’t – though strangely, my all-text emails/newsletters were still going out.
Now since I’ve got my SMTP correct, I experimented with sending out a newsletter containing a (600×400) image. Here’s the interesting part: _some_ of the recipients (mostly gmail accounts) did not receive it.
I think it has to do with the spam filtering, as you explained https://www.thenewsletterplugin.com/plugins/newsletter/newsletter-spam . The image _is_ hosted on the same server though.
So the conclusion that I am coming to is this: sending emails/newsletters out with embedded images _is_ risky in that things beyond your control can still silently drop your emails.