Item #: SCP-XXX
Object Class: Safe
Special Containment Procedures: Should instances of SCP-XXX be located outside of Foundation control, the surrounding soil is to be excavated and the fungal growth removed. Under no circumstances should any personnel place their hand or any other extremity inside SCP-XXX-1, any human flesh making contact with the insides of the box will be rapidly dissolved.
Description: SCP-XXX-1 has the outward appearance of a Lowe's PostMaster galvanized steel mailbox, painted in black. Upon closer inspection, it has been found to be composed not of metal, but of an uncharacterized iron-polysaccharide complex. The support post contains a digestive tract, used for filling the mailbox cavity with an acidic compound and transporting the resulting slurry down to the roots.
SCP-XXX is a fungal mycelium structure similar to that of the shiitake mushroom, on a much larger scale. It develops when a normal mailbox is pollinated by SCP-XXX-2, and can only grow when it dissolves and absorbs human flesh. Submerging a human hand in the acid for longer than 30 seconds will result in all skin and muscle being stripped from the bone. As SCP-XXX grows, it begins to absorb iron and other nutrients from the soil, resulting in the growth of SCP-XXX-1. As iron-deficient soil is a symptom of SCP-XXX infestation, active outbreaks may be detected by monitoring USDA soil survey reports.
SCP-XXX-2 are the spores required to spread the mailbox fungi. They arrive in a seemingly-normal envelope bearing the letterhead of the █████ █████ Gardening Supply Company, no return address provided. If the spores are left in a normal mailbox for a period of time no shorter than 30 minutes, they will begin to pollinate. As cross-pollination from two separate mailboxes is required for infection and growth of the fungus, the spread of SCP-XXX is progressing slowly.
Addendum: Pulling the mailbox flag up will induce a large expulsion of concentrated acid from the mail cavity, resulting in serious injury or death. The acid will quickly dissolve any plant-based organic compounds (such as cotton), and will then begin to dissolve skin and muscle tissue. Tests to determine said acid's usefulness in dissolving SCPs scheduled for destruction are ongoing.
Addendum: As of 01/06/20██, instances of SCP-XXX-1 no longer bear resemblance to the Lowe's PostMaster (black). They now resemble white Home Depot "Gibraltar Tuff Body Post-Mount" mailboxes. This change seems to have been a forced evolution based on our efforts to contain SCP-XXX. Mail delivery to suspected areas of SCP-XXX infection should be monitored more thoroughly.