A San Luis Obispo High School teacher on voluntary leave who allegedly referred to “going postal” in an email rant and then disrupted a continuation high school campus was arrested and charged with making criminal threats.

Brian Sanford Miller, 55, who has taught in the San Luis Coastal Unified School District for 26 years, allegedly made remarks that concerned district officials in an email he wrote to the San Luis Coastal Teachers Association on March 28.

Miller expressed frustration that district administrators were not listening to him and said the school board has “the spine of a jellyfish,” according to the email that’s part of his case file.

“If no one continues to pick up your pleas for help, well, there you have the reason for the term ‘going postal,’ ” the email said.

“Guys don’t snap one day and decide to shoot up their workplace instead of a convenience store.”

But Miller said they do when their pleas for help are ridiculed, according to the email.

The email continues to say, “I’m going to the office. I will probably die there. But three random people get to die with me.”

Miller has pleaded not guilty in San Luis Obispo Superior Court to attempted criminal threats, a felony; threatening a school employee, a felony; and disruptive presence at a school, a misdemeanor.

He’s in custody at County Jail in lieu of $1 million bail. As a way to better understand his mental state, Judge Michael Duffy appointed a psychologist to examine him as part of his defense after his arraignment earlier this month.

Miller is on a voluntary leave this year from San Luis Obispo High School and was interested in a job at Pacific Beach Continuation High School, said Ryan Pinkerton, the district’s director of personnel. But he wasn’t being considered for that move, Pinkerton said.

Pinkerton said Miller hadn’t shown dangerous behavior previously, though he was known to be outspoken about certain causes.

“Our biggest concern is safety of students and staff,” Pinkerton told The Tribune on Wednesday. “Whatever it takes for us to make sure kids are safe is most important.”

No specific reason for Miller’s anger is given in the email, but he notes a perceived lack of concern for Latino students compared with white students and a teacher being “run out of SLO High” while trying to help a frustrated kid.

Miller also expressed personal frustrations in the email, saying, “you yell at top volume because your job is in jeopardy, your mother just died, your kid went to jail, and not one person in SLO Coastal really gave a (expletive) about little old me.”

In a separate incident on March 29, Miller allegedly went to Pacific Beach around 8 a.m. and argued with Principal Greg Halfman, according to a San Luis Obispo Police Department report.

Miller claimed he was the school’s new math teacher, but Halfman checked with a district official who confirmed that he wasn’t, police said.

Halfman asked Miller several times to leave, the report states, and Miller was arrested shortly after the verbal exchange.

Pinkerton said that Miller’s job status won’t change as the district monitors the court proceedings.