---
title: "Mail Client Stops Receiving: Fail2ban IMAP Self-Ban"
domain: troubleshooting
category: networking
tags: [fail2ban, imap, dovecot, email, self-ban]
status: published
created: 2026-04-02
updated: 2026-04-02
---
# Mail Client Stops Receiving: Fail2ban IMAP Self-Ban

## 🛑 Problem

A mail client stops receiving new email on one device while other devices (e.g., phone on cellular) continue to work normally. The mail server is healthy — Postfix is delivering to maildir and Dovecot is running — but the affected device receives no new messages and is never prompted for credentials.

---

## 🔍 Diagnosis

### Step 1 — Confirm the mail server is delivering

```bash
ssh root@<mailserver> "tail -20 /var/log/maillog | grep 'status=sent'"
```

If you see `status=sent (delivered to maildir)`, the server is working. The issue is on the client side.

---

### Step 2 — Check if the client is connecting at all

```bash
ssh root@<mailserver> "grep '<client_ip>' /var/log/maillog | tail -10"
```

If there are **zero results**, the client is not reaching the server at all — not a credentials or sync issue.

---

### Step 3 — Get the client's current public IP

Run this on the affected machine:

```bash
curl -s https://api.ipify.org
```

---

### Step 4 — Check if that IP is banned by Fail2ban

```bash
ssh root@<mailserver> "fail2ban-client status postfix-sasl"
ssh root@<mailserver> "fail2ban-client status dovecot-invalid"
```

Look for the IP in the `Banned IP list`. If it's there, that's your problem.

---

### Step 5 — Find when the ban was applied

```bash
ssh root@<mailserver> "grep '<client_ip>' /var/log/fail2ban.log | tail -20"
```

This shows the exact timestamps of auth failures and the ban event.

---

## ✅ Fix

Unban the IP from all relevant jails:

```bash
fail2ban-client set postfix-sasl unbanip <IP>
fail2ban-client set dovecot-invalid unbanip <IP>
```

Mail should resume immediately without restarting any services.

---

## 🔁 Why This Happens

| Symptom | Cause |
|---|---|
| One device stops getting mail, others don't | Each device has a different public IP. Only the banned IP is blocked. |
| No auth prompt in the mail client | Fail2ban issues a TCP `REJECT` — the client sees a connection error, not an auth failure, so it doesn't prompt for new credentials. It silently retries on a timer. |
| Multiple failed attempts before ban | The mail client retried with a previously valid session token or stale auth state, triggering the `maxretry` threshold. |
| Ban on `postfix-sasl` blocks IMAP (port 993) | The `postfix-sasl` jail monitors ports 25, 465, 587, 143, 993, 110, and 995 — not just SMTP. A failed SMTP auth attempt can ban access to IMAP as well. |

---

## ⚠️ Key Notes

- **Fail2ban `postfix-sasl` covers all mail ports** — a single jail can lock out SMTP *and* IMAP simultaneously.
- **The affected device's IP is never logged in Dovecot** once banned — the rejection happens at the iptables/Fail2ban layer before Dovecot sees the connection.
- **Tailscale doesn't help** if the mail client connects via the public interface — the ban applies to the public IP, not the Tailscale IP.
- Check when the ban happened: `grep '<IP>' /var/log/fail2ban.log` shows exact timestamps.

---

## 🔎 Quick Diagnostic Commands

```bash
# Get your current public IP (run on affected machine)
curl -s https://api.ipify.org

# Check all Fail2ban jail statuses
fail2ban-client status

# Check a specific jail for a banned IP
fail2ban-client status postfix-sasl
fail2ban-client status dovecot-invalid

# Unban from a specific jail
fail2ban-client set postfix-sasl unbanip <IP>
fail2ban-client set dovecot-invalid unbanip <IP>

# Unban from all jails at once
for jail in $(fail2ban-client status | grep "Jail list" | sed 's/.*://;s/,/ /g'); do
  fail2ban-client set $jail unbanip <IP> 2>/dev/null && echo "Unbanned from $jail"
done

# Find when a specific IP was banned
grep '<IP>' /var/log/fail2ban.log | tail -20
```