Attachment too large for mailing - should there have been a warning?
There's an administrative setting that controls that limit here:

Administer -> System Settings -> Misc (Undelete, PDFs, Limits, Logging, Captcha, etc.)

The "syntax error" you are seeing is likely what the Civi mailer is getting back from the smtp server. I've seen that as a kind of catchall error message from mailers (e.g. it's what sparkpost will report when not configured). I don't think that Civi can do anything other than pass it on - i.e. the reporting error is from the system that's trying/failing to send out the mail.

Personally, I think there should be a message in the CiviMail system strongly discouraging attachments and encouraging attachments to be uploaded and linked to instead. That will increase deliverability.

The only really good use-case for attachments is if the document is private.

So the answer to your question is: "no".