A US school principal responded to a worried parent's query with a poop emoji.

It's hard to hit the right tone in emails, especially in a business setting, but resorting to emoji is not exactly advised, especially faecal ones.

The Miami Herald reported that when student mother Nancy Tyler emailed her concerns to Miami Arts Charter School's principal Alfredo de la Rosa, she was taken aback by the rude tone of his answer.

Tyler had written to inquire about her daughter's 8th grade teacher (year 9) absence and confirm whether he had left the school.

Her emailed also made reference to the arrest of a sexual predator on the school's other campus.

De la Rosa didn't take kindly to her questions and made it clear in his answer, which Tyler has shared with local media.

"Oh, you AGAIN," his email started, setting the tone.

"I believe you sent me a prior email once before about something you 'heard'. Of course, just like last time, you are wrong again," he continued. "But that is typical for you."

He then goes on to answer each point with passive aggression and sarcasm.

Tyler wrote she heard that her daughter had been sent to another class due to a teacher's absence and wanted De La Rosa to tell her whether the teacher had left the school for good. Instead, the school principal and founder wrote: "Actually, I don't understand because you are always complaining about things for little or no reason."

When the student's mother asked how she could "get her [daugher] a more stable learning environment", De La Rosa answered with: "You can try another school, maybe?"

After answering to each of Tyler's questions in a similar manner, De La Rosa signed his email with a poop emoji.

He has since then apologised, saying he didn't know how the emoji had made it into his email but admitte the general tone of his correspondence was bad form.

"I didn't do it intentionally," De La Rosa told the New York Post. "I realise it looks bad, but it was not intended to be on there. That would be a bit over the top."

He explained Tyler and him had been in contact often ever since her daughter joined the school, and that there was "history" between the two of them. He said that the mother "got under [his] skin" and that he should have let "cooler heads" prevail.

De La Rosa has since then sent an email of apology to all students' parents in order to make amends.

"In retrospect, I concede that the tone and content of my response to a recent parent email was not an effective way to react or communicate," he wrote.

"It is truly never my intention to alienate anyone who may wish to inquire about any issue or voice any concern at our school," he added.

Tyler said that she was upset with De La Rosa's answer. But she's not the only parent to complain about the principal. There's actually a whole Facebook page, titled "Unprofessional Leadership at MAC" dedicated to share parents' bad experiences with De La Rosa.

The principal has since then said he wouldn't comment on the situation in the media in fear of drawing negative attention to the parent's daughter.