@default(autoincrement()) not working on non id integer fields

I am having an id field in my model that is not primary but I want it to be a autoincrement field. So, for this, I just added @default(autoincrement()) in the front of my id field. But this is not working id is not autoincrementing and even I am not able to create if I did not explicitly pass the id filed. This is my model.

model Mail {
    id Int   @default(autoincrement())
    createdAt  DateTime   @default(now())
    updatedAt  DateTime   @updatedAt
    body String
    to String
    from String
    subject String
    messageId String @id
    date DateTime
    attachments Attachment[]
}