Yarmouth police are investigating at least two thefts of mail from the drive-up mailbox at the front of the post office on Forest Falls Drive.

The thefts likely occurred because the mailbox was overstuffed with letters and packages, allowing the thief or thieves easy access to any mail near the mail slot, police said Tuesday in a Facebook post.

Yarmouth police said they have received two reports in the past week of mail being stolen from the box. In each case, checks made out to pay bills were removed, and in one instance a check was fraudulently rewritten for a greater sum of money.

“We believe that overfilling the mailbox at this location is providing the individuals responsible for this with an easy crime of opportunity,” Yarmouth police said in a news release.

The Yarmouth postmaster is aware of the thefts and has said the Yarmouth post office has ordered a new anti-fishing mailbox. The postmaster also said the existing mailbox will be emptied more frequently from now on.

“This (emptying more often) is made more challenging by people leaving oversized packages in the mailbox, which causes it to fill up more quickly, especially on the weekends,” police said.

Police are encouraging people to drop off mail and packages inside the post office during regular business hours when the outside mailbox is full.

Forest Falls Drive is off Route 1 near the Hannaford supermarket and Royal River Park.