Considering it looks for repetitive email and blocks it, and the fact the printer is sending the same email every time and the only thing that changes is the size of the attachment, I would expect it to work once, maybe a few times, and then get blocked anyway.
The Printer sends the same message body, subject line, attachment name and footer on every single email.
Their SMTP settings look pretty straight forward.
But your printer, if it really isn't able to see the server, would have an issue in DNS,Gateway or the time is wrong (Add Proxy if you need one to access the internet)