Both these error messages fail the "where do we go from here?" test - disrespecting the user with requiring open ended work on their part.
Having some breadcrumbs to get back to the right track is much more valuable than flowery wordings. Eg: Message too large - failed to send email. Network unavailable - failed to send email. Subscription expired - failed to send email. Unexpected service outage - https://email.io/status - failed to send email.
The details of the error weren't the point of my example. And being that terse sounds like you're barking orders at the user. Once again, shortness is fine for programmer communication, but personally for an end user just going about their day I would avoid such an impertinent tone.
Having some breadcrumbs to get back to the right track is much more valuable than flowery wordings. Eg: Message too large - failed to send email. Network unavailable - failed to send email. Subscription expired - failed to send email. Unexpected service outage - https://email.io/status - failed to send email.