Absolutely not! It would have had greater effect if it read (and I work without context):
Your boss doesn't appear to appreciate the requirements of operating an SMTP relayhasn't given you any substantive reason, in saying this. Consider You should definitely ask for more details (we can't possibly give an ASA or somethinganswer with just this), and also consider finding a new job if you're being put in situations like thisit is a consistent and serious problem it might be better for you professionally to seek employment elsewhere. You could also just let it go.
The cumulative effect of the comment as quoted by Iain is such that it has no redeeming merit and the flag should have been accepted; it is not a constructive or professional comment even in our profession.