Locate your Postfix configuration file. A common location is /etc/postfix/main.cf.

Open the main.cf file with a text editor and add the following to the configuration.

smtp_sasl_auth_enable = yes

smtp_sasl_password_maps = static:_Your SendGrid Username_:_Your SendGrid Password_

smtp_sasl_security_options = noanonymous

smtp_tls_security_level = encrypt

header_size_limit = 4096000

relayhost = [smtp.sendgrid.net]:587

Save and close the /etc/postfix/main.cf file.

Restart Postfix by using this command:

/etc/init.d/postfix restart

If you get the "no mechanism available" error, verify that you have all of the necessary libraries for authentication or encryption. You can install these libraries by using the following commands:

For Debian and Ubuntu, use this command: apt-get install libsasl2-modules

For Red Hat and CentOS, use this command: yum install cyrus-sasl-plain

After you install these libraries, use the same restart command:

/etc/init.d/postfix restart

If port 587 does not work, use port 2525 in the Postfix configuration. You might also need to open the configuration file /etc/postfix/main.cf and uncomment the following line:

#tlsmgr unix - - n 1000? 1 tlsmgr