An adjustable mounting bracket for mounting a mailbox, the mounting bracket including a first side section configured to contact one side of the mailbox and having one or more first anchoring portions extending inwardly from the first side section to contact a supporting body, and a second side section configured to contact another side of the mailbox and having one or more second anchoring portions extending inwardly from the second side section to contact the supporting body, wherein the first and second anchoring portions are configured to contact the supporting body without overlapping.