Send mail from local host using postfix on MacOS High Sierra.

postfix_mail_macosx.md

Setting up postfix on MacOS High Sierra

MacOS Sierra High comes with preinstalled postfix. Follow these steps to configure it on a local system:

1. Create a sasl_passwd file

sudo nano /etc/postfix/sasl_passwd

• Add this to the file

smtp.gmail.com:587 [email protected]:PASSWORD

Replace EMAIL with your gmail username and replace PASSWORD with your gmail password.

• Create a lookup table

sudo postmap /etc/postfix/sasl_passwd

2. Edit the main.cf file

• Open postfix's main.cf

sudo nano /etc/postfix/main.cf

• Edit these values if they are not set already

mail_owner = _postfix
setgid_group = _postdrop

• Add these fields at the end of the file (I am choosing mtp.gmail.com as myrelayhost to send email from gmail account. You can choose any other SMTP relayhost)

#Gmail SMTP
relayhost=smtp.gmail.com:587
# Enable SASL authentication in the Postfix SMTP client.
smtp_sasl_auth_enable=yes
smtp_sasl_password_maps=hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options=noanonymous
smtp_sasl_mechanism_filter=plain
# Enable Transport Layer Security (TLS), i.e. SSL.
smtp_use_tls=yes
smtp_tls_security_level=encrypt
tls_random_source=dev:/dev/urandom

3. Enable less secure app access

If you are using gmail then you must have to enable less secure app access.

4. Set postfix to autorun on reboot

• Disable SIP

• Open /System/Library/LaunchDaemons/com.apple.postfix.master.plist

sudo nano /System/Library/LaunchDaemons/com.apple.postfix.master.plist

• Remove these lines

<string>-e</string>
<string>60</string>

and add these lines

<key>KeepAlive</key>
<true/>

• Reload and relaunch the deamon

sudo launchctl unload /System/Library/LaunchDaemons/com.apple.postfix.master.plist
sudo launchctl load /System/Library/LaunchDaemons/com.apple.postfix.master.plist

• Enable SIP

5. Send mail

Test by sending a mail

echo "Postfix setting test" | mail -s "Hello Postfix" "[email protected]"

Replace [email protected] with the email id of recipent.

Some useful commands

• mailq : Check mails in the queue and errors if mail not sent.
• sudo postfix flush: Flush the queue.
• sudo postsuper -d ALL Delete mails in the queue.
• sudo rm /var/mail/$USER Remove all mails from local host.
• sudo postfix start Start postfix mail system.
• sudo postfix stop Stop postfix mail system.
• sudo postfix reload Reload postfix mail system.

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References:

1. How to send emails from localhost.
2. Postfix auto start on Sierra for smtp relay.

I'm kinda worried that you need to disable SIP. Does that mean that Apple installs postfix, but it's not intended to be used?

@raarts
"Does that mean that Apple installs postfix, but it's not intended to be used?": No. It doesn't actually mean that. If you are doing any changes to /System directory then apple expects that you know what you are doing and it forces you to disable SIP to make any changes (as SIP is intended to enhance security of Mac).