---
title: Configuring Sendmail for Laravel
description: Sendmail is a classic Mail Transfer Agent (MTA) with a long history in Unix-based systems. While modern alternatives like Postfix and Exim dominate new deployme
---

# Configuring Sendmail for Laravel

## Overview

Sendmail is a classic Mail Transfer Agent (MTA) with a long history in Unix-based systems. While modern alternatives like Postfix and Exim dominate new deployments, Sendmail remains valuable for legacy systems, deep customization, and specific integration scenarios.

**This guide is not a recommendation to use Sendmail everywhere**, but rather a comprehensive reference for developers who need to configure it—whether working with legacy systems, complex requirements, or custom mail handling.

### When to Use Sendmail

✅ **Good use cases:**
- Integrating with existing Sendmail infrastructure
- Advanced customization and local mail handling
- Legacy systems requiring Sendmail compatibility
- Direct SMTP control without external services

❌ **Not recommended for:**
- New deployments (use Postfix or Exim instead)
- Simple hosting setups (use managed SMTP services)
- Beginners (Postfix is much simpler)

---

## System Requirements

Before installing Sendmail, ensure:

| Component | Requirement | Notes |
|-----------|-------------|-------|
| **OS** | Linux, BSD, macOS | Unix-based systems only |
| **RAM** | 256 MB minimum | 512 MB+ recommended |
| **Disk** | 1 GB minimum | For queue and logs |
| **m4 macro processor** | Required | `sudo apt-get install m4` |
| **PHP** | 5.2+ | For `proc_open()` function |

### Key Limitation

**Important:** Laravel's Sendmail transport uses `proc_open()`, a PHP function that must be enabled. If disabled in `php.ini` (common in shared hosting), you cannot use Sendmail with Laravel.

---

## Installation

### Install Sendmail

**Ubuntu/Debian:**
```bash
sudo apt-get update
sudo apt-get install sendmail sendmail-bin m4
sudo systemctl enable sendmail
sudo systemctl start sendmail
```

**CentOS/RHEL:**
```bash
sudo yum install sendmail sendmail-cf m4
sudo systemctl enable sendmail
sudo systemctl start sendmail
```

**Verify installation:**
```bash
sendmail -v
```

---

## Understanding Sendmail Configuration

### `.mc` vs `.cf` Files

Sendmail's configuration system is unique and often confusing:

| File Type | Purpose | Editable? |
|-----------|---------|-----------|
| **`.mc` file** | Human-readable configuration | ✅ Yes (edit this) |
| **`.cf` file** | Compiled by m4; used by Sendmail | ❌ No (don't edit directly) |

**The workflow:**
```
.mc file → m4 processor → .cf file → Sendmail reads .cf
```

### The m4 Macro Processor

Sendmail uses `m4` to compile `.mc` files into `.cf` files. Key concepts:

- **Processes as stream** — Order of directives matters
- **`dnl` command** — "Delete through newline"; used for comments
- **Macro expansion** — Happens even in comments; can cause surprises

**Convert .mc to .cf:**
```bash
m4 /etc/mail/cf/m4/cf.m4 sendmail.mc > sendmail.cf
```

---

## Basic `.mc` File Structure

A proper Sendmail `.mc` file follows this order:

```m4
# Version control
VERSIONID(`$Id: example.mc,v 1.0 2024/01/01 $')dnl

# Operating system (REQUIRED)
OSTYPE(`linux')dnl

# Domain configuration (optional but recommended)
DOMAIN(`generic')dnl

# Feature definitions (must come before MAILER)
FEATURE(`use_cw_file')dnl
FEATURE(`mailertable')dnl
FEATURE(`virtusertable')dnl

# Macro definitions (depends on FEATURE)
define(`SMART_HOST', `smtp.example.com')dnl
define(`MAIL_HUB', `mail.example.com')dnl

# Local customizations
LOCAL_CONFIG
# Custom rules here

# Mailer definitions (MUST BE LAST)
MAILER(`local')dnl
MAILER(`smtp')dnl
```

**Critical rule:** Place `MAILER()` directives last. Features that depend on macros must come before those macros are used.

---

## Essential Configuration Directives

### OSTYPE (Required)

Specifies the operating system. This is **mandatory** and controls paths, flags, and defaults.

```m4
OSTYPE(`linux')dnl
```

**Common values:**
- `linux` — Linux systems
- `bsd44` — BSD variants
- `solaris` — Solaris/SunOS
- `hpux` — HP-UX
- `aix` — IBM AIX

Without `OSTYPE`, the build will fail.

### DOMAIN (Optional but Recommended)

Sets domain-specific configurations like local names and masquerading:

```m4
DOMAIN(`generic')dnl
```

Or custom domain (create `/etc/mail/domain/example.com.m4`):

```m4
DOMAIN(`example.com')dnl
```

### MAILER (Required)

Defines which mailers Sendmail uses. `local` is included by default, but you must explicitly include `smtp` for outgoing mail:

```m4
MAILER(`local')dnl
MAILER(`smtp')dnl
```

**Available mailers:**
- `local` — Local delivery (included automatically)
- `smtp` — SMTP variants (smtp, esmtp, smtp8, dsmtp, relay)
- `uucp` — UUCP delivery (legacy)
- `procmail` — Pipe to procmail
- `cyrus` — Cyrus mailbox format
- `fax` — HylaFAX delivery

### FEATURE Macros

Enable optional functionality:

```m4
FEATURE(`use_cw_file')dnl           # Read /etc/mail/local-host-names
FEATURE(`use_ct_file')dnl           # Read trusted users
FEATURE(`mailertable')dnl           # Enable mailer table routing
FEATURE(`virtusertable')dnl         # Virtual domain hosting
FEATURE(`always_add_domain')dnl     # Add domain to local addresses
FEATURE(`generics_entire_domain')dnl # Apply generics to subdomains
```

---

## Configuration for Laravel

### Step 1: Create/Edit `.mc` File

Create `/etc/mail/sendmail.mc`:

```m4
VERSIONID(`$Id: sendmail.mc,v 1.0 2024/01/01 $')dnl
OSTYPE(`linux')dnl
DOMAIN(`generic')dnl

FEATURE(`use_cw_file')dnl
FEATURE(`mailertable')dnl
FEATURE(`always_add_domain')dnl

define(`confLOG_LEVEL', `9')dnl
define(`confDOMAIN_NAME', `example.com')dnl

LOCAL_CONFIG
# Local rules can go here

MAILER(`local')dnl
MAILER(`smtp')dnl
```

### Step 2: Compile to `.cf` File

```bash
cd /etc/mail
m4 m4/cf.m4 sendmail.mc > sendmail.cf
sudo chown root:wheel sendmail.cf
sudo chmod 644 sendmail.cf
```

### Step 3: Restart Sendmail

```bash
sudo systemctl restart sendmail
```

### Step 4: Configure Laravel

Update `.env`:

```env
MAIL_MAILER=sendmail
MAIL_SENDMAIL="/usr/sbin/sendmail -bs"
```

Update `config/mail.php`:

```php
return [
    'default' => env('MAIL_MAILER', 'sendmail'),
    'mailers' => [
        'sendmail' => [
            'transport' => 'sendmail',
            'path' => env('MAIL_SENDMAIL', '/usr/sbin/sendmail -bs'),
        ],
    ],
];
```

Clear Laravel's configuration cache:

```bash
php artisan config:cache
```

---

## Address Rewriting and Masquerading

### Masquerading (Hiding Internal Addresses)

Rewrite outgoing mail addresses to appear to come from your domain:

```m4
MASQUERADE_AS(`example.com')dnl
FEATURE(`masquerade_envelope')dnl  # Masquerade envelope too
```

**Example:**
- Internal user: `john@mail.example.com`
- Appears as: `john@example.com`

### Masquerade Exceptions

Exclude certain hosts from masquerading:

```m4
MASQUERADE_EXCEPTION(`localhost')dnl
MASQUERADE_EXCEPTION(`mail.example.com')dnl
```

### Generic Maps (Address Rewriting)

Rewrite local addresses to different domains:

**Create `/etc/mail/genericstable`:**

```
root                admin@example.com
www-data            web@example.com
@localhost          user@example.com
```

**Add to `.mc` file:**

```m4
FEATURE(`generics_entire_domain')dnl
define(`GENERICS_TABLE_DOMAIN_NAMES', `example.com')dnl
```

**Build the map:**

```bash
makemap hash /etc/mail/genericstable < /etc/mail/genericstable
sudo systemctl restart sendmail
```

---

## Virtual Domains

### Virtual User Table

Host multiple domains without creating system users:

**Create `/etc/mail/virtusertable`:**

```
support@example.com         localuser
admin@example.net           admin@example.com
error@another.org           /dev/null
info@              error    "550 No such user here"
```

**Add to `.mc` file:**

```m4
FEATURE(`virtusertable')dnl
```

**Build the map:**

```bash
makemap hash /etc/mail/virtusertable < /etc/mail/virtusertable
sudo systemctl restart sendmail
```

**Map entries explained:**
- `address@domain    username` — Deliver to local user
- `address@domain    user@other.com` — Forward to external address
- `address@domain    /dev/null` — Silently discard
- `@domain    error "message"` — Reject with error message

---

## Relaying and Routing

### Smart Host (Central Relay)

Send all outgoing mail through a relay server:

```m4
define(`SMART_HOST', `smtp.isp.com')dnl
```

### Mail Hub (Local Host Relay)

Send mail for local hostnames to a central hub:

```m4
define(`MAIL_HUB', `mailhub.example.com')dnl
```

### Local Relay (Unqualified Names)

Forward unqualified addresses (just username) to a relay:

```m4
define(`LOCAL_RELAY', `relay.example.com')dnl
```

---

## Mailer Tables

Route mail for specific domains to different mail servers:

**Create `/etc/mail/mailertable`:**

```
.example.com        smtp:mail.example.com
partner.com         smtp:[partner-mail.com]:2525
legacy.org          uucp-new:legacyhost!
.                   smtp:[smtp.isp.com]
```

**Add to `.mc` file:**

```m4
FEATURE(`mailertable')dnl
```

**Build the map:**

```bash
makemap hash /etc/mail/mailertable < /etc/mail/mailertable
sudo systemctl restart sendmail
```

**Syntax:**
- `.domain` — Matches domain and subdomains
- `domain` — Exact match only
- `.` — Default/catch-all

---

## Security Configuration

### TLS/STARTTLS

Enable encrypted SMTP connections:

```m4
define(`confCACERT_PATH', `/etc/ssl/certs')dnl
define(`confCACERT', `/etc/ssl/certs/ca-certificates.crt')dnl
define(`confSERVER_CERT', `/etc/letsencrypt/live/mail.example.com/fullchain.pem')dnl
define(`confSERVER_KEY', `/etc/letsencrypt/live/mail.example.com/privkey.pem')dnl
```

### SMTP Authentication

Allow authenticated relay (combat spam):

```m4
define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
define(`confAUTH_OPTIONS', `A p')dnl
```

### Anti-Spam Rules

Restrict relaying to authorized users:

```m4
FEATURE(`relay_hosts_only')dnl
FEATURE(`loose_relay_check')dnl

LOCAL_CONFIG
R$*                $: $&\&#123;client_name\&#125;
```

---

## Custom Rulesets

### LOCAL_RULE_3 (Canonicalization)

Customize address canonicalization:

```m4
LOCAL_RULE_3
# Map old hosts to new domains
R$* @ oldhost $*    $1 @ newhost.example.com $2
```

### LOCAL_RULESETS (Custom Rules)

Add completely custom rulesets:

```m4
LOCAL_RULESETS

Scheck_from_ok
R$*                $: ok
```

### LOCAL_CONFIG (Custom Declarations)

Define custom maps and variables:

```m4
LOCAL_CONFIG
KscheduleMap hash -o /etc/mail/schedulemap
Kldap ldap -1 -v sendmailMTAmap -b dc=example,dc=com
```

---

## Using Lookup Tables

### Berkeley DB Maps

Default map type for most Sendmail configurations:

```bash
makemap hash /etc/mail/mapname < /etc/mail/mapname.txt
```

### Change Default Map Type

```m4
define(`DATABASE_MAP_TYPE', `dbm')dnl
```

### LDAP Integration

Query LDAP directory for lookups:

```m4
LOCAL_CONFIG
Kldap_aliases ldap -1 -v mail -b ou=aliases,dc=example,dc=com
Kldap_users ldap -1 -v mailLocalAddress -b ou=people,dc=example,dc=com
```

---

## Troubleshooting Sendmail

### Check Sendmail Status

```bash
sudo systemctl status sendmail
netstat -tulnp | grep sendmail
```

### View Sendmail Logs

```bash
# Real-time monitoring
sudo tail -f /var/log/mail.log

# Search for errors
grep "ERROR" /var/log/mail.log

# Find rejected mail
grep "reject" /var/log/mail.log

# Trace a specific message
grep "MESSAGE_ID" /var/log/mail.log
```

### Increase Log Level

Add to `.mc` file:

```m4
define(`confLOG_LEVEL', `9')dnl
```

Then recompile and restart.

### Test Email Sending

Manually test Sendmail:

```bash
echo "Subject: Test Email

This is a test." | sendmail -v recipient@example.com
```

### Verify Configuration

Check syntax before restarting:

```bash
sendmail -C /etc/mail/sendmail.cf -bi
```

### Common Issues and Solutions

**Issue: "sendmail not found"**
```bash
sudo apt-get install sendmail sendmail-bin
```

**Issue: "Emails not sending from Laravel"**
- Check `proc_open()` is not disabled in `php.ini`
- Verify `/usr/sbin/sendmail` exists and is executable
- Check web server user can execute sendmail
- Review logs: `tail -f /var/log/mail.log`

**Issue: "Permission denied on sendmail"**
```bash
sudo chmod 4755 /usr/sbin/sendmail
sudo chown root:smmsp /usr/sbin/sendmail
```

**Issue: ".cf file not found" errors**
- Ensure you compiled `.mc` to `.cf`: `m4 /etc/mail/cf/m4/cf.m4 sendmail.mc > sendmail.cf`
- Restart Sendmail after moving `.cf` file
- Check file permissions: `sudo chmod 644 /etc/mail/sendmail.cf`

**Issue: "Relay access denied"**
- Check SMART_HOST configuration
- Verify MASQUERADE_AS is set if needed
- Review access database: `makemap -q hash /etc/mail/access`

---

## Working with the Mail Queue

### View Queue

```bash
# List all queued messages
mailq

# Count messages
mailq | wc -l

# Show just message IDs
mailq | grep "^[A-F0-9]"
```

### Flush Queue (Force Delivery)

```bash
# Retry all messages
sendmail -q

# Force immediate processing
sendmail -q -v

# Process specific queue run
sendmail -qI <QUEUE_ID>
```

### Remove Stuck Messages

```bash
# Remove specific message
sudo rm /var/spool/postfix/deferred/<QUEUE_ID>

# Clear entire queue (dangerous!)
sudo rm /var/spool/postfix/deferred/*
```

---

## System Mail Forwarding

Redirect system mail (cron, services) to real person:

**Create/Edit `/etc/aliases`:**

```
root: admin@example.com, admin@backup-domain.com
www-data: web-admin@example.com
```

**Build the alias database:**

```bash
sudo newaliases
```

This ensures important system messages reach administrators, not root's inbox.

---

## Performance Tuning

### Connection Settings

```m4
define(`confTO_CONNECT', `10s')dnl
define(`confTO_INITIAL', `10s')dnl
define(`confTO_QUEUERETURN', `5d')dnl
define(`confMAX_HEADERS_LENGTH', `32768')dnl
```

### Concurrency Limits

```m4
define(`confMAX_DAEMON_CHILDREN', `20')dnl
define(`confMAX_QUEUE_CHILDREN', `20')dnl
define(`confQUEUE_LA', `8')dnl
define(`confREFUSE_LA', `12')dnl
```

### Process Limits

```m4
define(`confMAX_MESSAGE_SIZE', `100000000')dnl
define(`confNO_RCPT_ACTION', `add-to-undisclosed')dnl
```

---

## Best Practices

### Configuration Management

✅ **Do:**
- Keep `.mc` files in version control
- Backup `/etc/mail/sendmail.cf` before changes
- Test configuration in development first
- Document all customizations
- Use `m4` to compile, never edit `.cf` directly

❌ **Don't:**
- Edit `.cf` files directly
- Forget to rebuild when modifying `.mc`
- Use Sendmail on shared hosting (if `proc_open` is disabled)
- Keep passwords in `.mc` files unencrypted

### Security Checklist

- [ ] Run Sendmail as unprivileged user (sendmail)
- [ ] Restrict file permissions: `chmod 600` for sensitive files
- [ ] Enable TLS for SMTP connections
- [ ] Implement SASL authentication for relaying
- [ ] Configure SPF and DKIM records
- [ ] Monitor logs regularly
- [ ] Keep Sendmail updated
- [ ] Test open relay prevention

### Monitoring

Regular checks to perform:

```bash
# Queue health
mailq | grep "^[A-F0-9]" | wc -l

# Recent errors
grep "ERROR" /var/log/mail.log | tail -20

# Authentication attempts
grep "AUTH" /var/log/mail.log | tail -10

# Rejected messages
grep "reject" /var/log/mail.log | tail -10
```

---

## Advanced Topics

### LDAP-Based Routing

Implement LDAP-based email routing with:

```m4
FEATURE(`ldap_routing')dnl
LOCAL_CONFIG
Kldaproute ldap -1 -v mailLocalAddress
```

### Mail Filters (Milters)

Integrate SpamAssassin or other mail filters:

```m4
define(`confINPUT_MAIL_FILTERS', `spamcheck')dnl
define(`confMILTER_DEFAULT_ACTION', `accept')dnl
```

### Queue Groups

Organize queue by destination:

```m4
QUEUE_GROUP(`fast', `P=/var/spool/mqueue-fast, F=')dnl
QUEUE_GROUP(`slow', `P=/var/spool/mqueue-slow, F=')dnl
```

---

## Migration Guide

### From Sendmail to Postfix

If moving away from Sendmail:

1. Back up all Sendmail configs and maps
2. Set up Postfix with equivalent configuration
3. Test mail flow on development system
4. Plan cutover during low-traffic window
5. Monitor logs for issues
6. Keep Sendmail running as backup initially
7. Redirect SMTP port to Postfix when confident

---

## Quick Reference

### Common `.mc` Directives

```m4
VERSIONID(`...')           # Version control
OSTYPE(`linux')            # Operating system
DOMAIN(`generic')          # Domain configuration
FEATURE(`use_cw_file')     # Read /etc/mail/local-host-names
FEATURE(`mailertable')     # Enable mailer routing
FEATURE(`virtusertable')   # Virtual domains
MAILER(`local')            # Local delivery
MAILER(`smtp')             # SMTP delivery
define(`SMART_HOST', `...')        # Relay server
define(`MASQUERADE_AS', `...')     # Masquerade domain
```

### Common Files

- `/etc/mail/sendmail.mc` — Source configuration
- `/etc/mail/sendmail.cf` — Compiled configuration
- `/etc/mail/local-host-names` — Accepted hostnames
- `/etc/mail/genericstable` — Address rewriting
- `/etc/mail/virtusertable` — Virtual domains
- `/etc/mail/mailertable` — Routing rules
- `/etc/aliases` — Local aliases
- `/var/log/mail.log` — Sendmail logs
- `/var/spool/mqueue/` — Mail queue

### Common Commands

```bash
m4 /etc/mail/cf/m4/cf.m4 sendmail.mc > sendmail.cf    # Compile
makemap hash /etc/mail/mapname < /etc/mail/mapname.txt # Build maps
newaliases                                               # Rebuild aliases
sendmail -C /etc/mail/sendmail.cf -bi                   # Verify
mailq                                                     # View queue
sendmail -q                                               # Flush queue
sudo systemctl restart sendmail                          # Restart
```

---