A suspect was quickly apprehended, and no one was wounded in the Thursday night gunfire.
The large mail processing area where the shootings took place was expected to reopen after 8 a.m. CST Friday, postal officials said.
"The best news is that nobody was hurt and the local police responded quickly," Postal Service spokesman Tony Robinson said Friday morning. "Management quickly had the building evacuated, which helped minimize the potential threat to the people."
The ordeal began around 6:38 p.m., when post office employees called 911 reporting gunshots. A large contingent of police were at a nearby mall because of holiday crowds and had a suspect in custody within 10 minutes, Montgomery Police Chief Kevin Murphy said.
The suspect was in his late 20s or early 30s, Murphy said. He didn't name the suspect and said federal postal officials would decide on charges.
On Friday, as workers prepared to reopen the processing facility, Robinson said counselors would be available during the day for employees who wished to talk about the shootings.
Robinson said authorities planned to check Friday whether video surveillance captured the gunfire. He said he didn't have further information on the suspect.
"We're thankful that the person was apprehended quickly enough that no life was lost," Robinson said.
Martin reported from Atlanta.