A teacher snooped on her colleagues' emails to see if they were talking about her following a row about cancelled leave, a court has heard.
Donna-Maria Thomas, 45, is accused of illegally accessing up to six accounts while working at Aldingbourne Primary School in Westergate, West Sussex.
Ms Thomas denied securing unauthorised access to the material and appeared at Portsmouth Crown Court earlier.
The prosecution said a "feud" had developed after a "misunderstanding".
Prosecutor Paul Fairle told socially-distanced jurors that Ms Thomas, of Bosham in West Sussex, had booked holiday and flights.
However, head teacher Liz Webster "realised a mistake had been made" and "felt she could not authorise" the leave.
After this point, he added, "it appears the relationship very much soured".
Mr Fairley said "hacking is probably a step too far" to describe the accusations, which date between December 2018 and January 2019.
He said Ms Thomas had also complained about Ms Webster on various occasions to the chair of the school governors.
"There were allegations made that might be termed whistleblowing, in terms of possible inconsistencies of the ways that the Key Stage One testing process was being administered," he added.
The trial continues.