PORTLAND, Ore. — When you see hundreds of thousands of pieces of mail come through every day, you start to know what to look for according to U.S. Postal Inspector Adam Sale.

“Our employees are the first line of defense for these types of situations,” explained U.S. Postal Inspector Adam Sale. “They see hundreds of thousands of pieces of mail a day and they can often very quickly pick out items that seem suspicious or out of the ordinary.”

Out of the ordinary could mean a number of things. Employees are trained to check if the package is uneven or bulky. Does it have a strange smell? Is the packaging discolored or stained? Is there a return address? Is it addressed to a title or an individual? Are words misspelled? If the answer to any of those questions is yes, it could signal a threat.

Jamie Partridge delivered mail in Northeast Portland for 25 years. He is now retired, but still remembers getting trained to look for suspicious packages.

"It's a dangerous job, not just dog bites, but chemicals and explosive devices in the mail,” explained retired letter carrier, Jamie Partridge.

With the explosive devices discovered this week, letter carriers underwent mandatory safety talks Wednesday morning. They were also shown a photo of one of the suspicious packages.

Postal Inspector Adam Sale also recommends businesses screen mail a little more carefully.

“It's always important to be vigilant if you are a large company, pretty much every large company has someone who's not happy about their business and so we encourage mail rooms at companies like yours and large companies to look at their mail every day,” Sale said.

Staff at city hall in Portland said they are currently putting together training for front desk personnel on handling packages.

The Democratic Party of Oregon said their local offices already have strict screening processes in place for mail. However, they did start locking their front doors this week for added security.

As for letter carriers, Partridge said they will likely be on alert.

“It's scary carrying stuff these days and you don't know who's going to use postal workers as their way of hiding the fact that they're attacking somebody,” Partridge said.