People living in Strathmore and surrounding communities are being warned that the security of their mailboxes might have been compromised.
A set of keys was stolen from the Strathmore Canada Post office on Thursday, RCMP said.
The female culprit fled in a white, newer-model Dodge pickup truck, police said.
Residents in the town of Strathmore and surrounding areas including Langdon and Dalemead are being advised to get their mail as soon as possible.
Canada Post is working to replace all affected locks in these areas.