---
title: Email
description: Anti-spam and mail protection for advmfr.net.
icon: Mail
---
Mail-borne malware and spam mitigation on the shared-hosting account behind
`advmfr.net`, 87 mailboxes.
**Core principle: zero mail loss.** No filter ever discards a message before it
has proven, in the central Quarantine folder, that it only catches spam.
## How a message reaches an inbox
Four layers act on every incoming message, and only one of them is ours.
Confusing them is the most common way to misdiagnose a delivery problem.
```mermaid
flowchart TD
A[Incoming message] --> B{o2switch upstream layer}
B -->|Extreme score| R[Rejected at SMTP with 550
never reaches the account
invisible in Track Delivery]
B -->|Everything else| C{Global Email Filters
ours, run top to bottom}
C -->|Executable or macro attachment| Q[Quarantine folder
system account]
C -->|Spam score 10 or above| Q
C -->|No match| D{o2switch antispam
per mailbox}
D -->|Detected| S[The user's own Spam folder]
D -->|Clean| I[Inbox]
```
The layer that matters when something goes missing is rarely the one people
assume. A message rejected upstream leaves **no trace at all**: not in
Quarantine, not in Track Delivery. A message in a user's Spam folder was never
touched by our filters. Only the middle box is configured by us.
## Start here