When attempting to run Postfix on macOS Yosemite, many developers encounter the critical error:

postfix/master[39799]: fatal: bind fe80::1 port 25: Can't assign requested address

This occurs because Postfix tries to bind to the IPv6 loopback address (fe80::1) by default, which isn't properly configured in Yosemite's network stack.

macOS Yosemite has known IPv6 implementation quirks. The fe80::1 address is technically a link-local address, not a true loopback like ::1. When Postfix attempts to bind to it, the OS rejects the request with EADDRNOTAVAIL.

Solution 1: Force IPv4 Only

Edit /etc/postfix/main.cf:

inet_protocols = ipv4
inet_interfaces = 127.0.0.1

Then restart Postfix:

sudo postfix stop
sudo postfix start

Solution 2: Proper IPv6 Configuration

If you need IPv6 support, first verify your interface:

ifconfig | grep inet6

Then modify main.cf:

inet_interfaces = localhost
inet_protocols = all

For system-level integration, create /Library/LaunchDaemons/org.postfix.master.plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>org.postfix.master</string>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/libexec/postfix/master</string>
        <string>-c</string>
        <string>/etc/postfix</string>
        <string>-D</string>
    </array>
    <key>EnvironmentVariables</key>
    <dict>
        <key>MAIL_CONFIG</key>
        <string>/etc/postfix</string>
    </dict>
    <key>QueueDirectories</key>
    <array>
        <string>/usr/libexec/postfix/queue</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>AbandonProcessGroup</key>
    <true/>
</dict>
</plist>

Then load it:

sudo launchctl load -w /Library/LaunchDaemons/org.postfix.master.plist

After applying any solution, verify Postfix is running:

sudo lsof -i :25

Check logs for errors:

tail -f /var/log/mail.log

Test SMTP locally:

telnet localhost 25

---

When attempting to run Postfix on macOS Yosemite, you might encounter the following error in your logs:

*** postfix/master[39799]: fatal: bind fe80::1 port 25: Can't assign requested address

This occurs because Postfix is trying to bind to the IPv6 loopback address (fe80::1) but fails due to system configuration issues.

macOS Yosemite has some peculiarities with IPv6 configuration:

• The fe80::1 address might not be properly assigned to your loopback interface
• IPv6 might be disabled at the system level
• Postfix configuration might be forcing IPv6 when it's not available

Edit your main.cf file:

sudo nano /etc/postfix/main.cf

Add or modify these lines:

inet_protocols = ipv4
inet_interfaces = loopback-only

Then restart Postfix:

sudo postfix stop
sudo postfix start

If you need IPv6 support, first verify your interfaces:

ifconfig lo0

You should see something like:

lo0: flags=8049 mtu 16384
    inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1 

If the IPv6 address is missing, you can add it manually:

sudo ifconfig lo0 inet6 fe80::1 prefixlen 64 alias

After making changes, verify Postfix is listening correctly:

sudo lsof -i :25

You should see output similar to:

COMMAND   PID USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
master  12345 root   12u  IPv4 0xabcdef123456789      0t0  TCP localhost:smtp (LISTEN)

To make the IPv6 loopback address persistent across reboots, create or edit:

sudo nano /etc/rc.local

Add this line:

ifconfig lo0 inet6 fe80::1 prefixlen 64 alias

Make the file executable:

sudo chmod +x /etc/rc.local

If you're still having issues, try these diagnostic commands:

postconf -n
netstat -an | grep 25
sysctl net.inet6.ip6.forwarding