Email Postfix email for multiple domains

Centmin Mod doesn't configure per domain emails see @yourdomain.com email hosting - CentminMod.com LEMP Nginx web stack for CentOS If you mean for email out, generally you'd use 3rd party transactional email providers like Amazon SES etc for better email deliverability and protecting your own site's IP reputation.

big discussion at Email - Mandrill users will be required to have a paid monthly MailChimp account | Centmin Mod Community

 

Postfix is configured for sending out emails for all domains out of box. So you're all taken care of for any site hosted on your server for Postfix outgoing emails sent from the main host name so emails sent from @mainhost.domain.com. Which is why Getting Started Guide step 1 for proper main hostname DNS configuration is important for properly email delivery via Postfix and also mentioned at Email - Steps to ensure your site/server email doesn't end up in spam inboxes | Centmin Mod Community

But I have no intention of doing any local email pop3/imap support on Centmin Mod for receiving emails as I don't want to bother with troubleshooting mail delivery issues as there's so many factors outside of my control as to why mail isn't delivered on the internet. I don't plan on providing any free support for such email related matters either. So best to use 3rd party email providers for @yourdomain.com emails for best uptime, reliability, security and anti-spam and email user management. See a list of recommendations at Email - Free @yourdomain.com Email Accounts & Alternatives

Tecmint actually has a 5 part article on setting up your @domain.com emails on CentOS 7 but part of their steps assume Apache web server instead of Nginx i.e. for phpmyadmin (centmin mod has it's own phpmyadmin.sh addon installer) and use of firewalld instead of Centmin Mod's CSF Firewall (which already setup proper whitelisted ports). But most of the email site setup is applicable. For properly postfix @domain handling you need to utilise MySQL, anti-virus/malware scanner and implement anti-spam management = all these can increase server resource usage dramatically. Virus scanning can blow out to an extra 4-8GB of memory and alot more cpu usage and local email disk storage will increase.

• Part 1: How to Create and Setup Postfix Mail Server Database (MariaDB) Securely
• Part 2: How to Configure Postfix and Dovecot with Virtual Domain Users in Linux
• Part 3: How to Add Antivirus and Spam Protection to Postfix Mail Server with ClamAV and SpamAssassin
• Part 4: How to Install and Configure RoundCube Webmail Client with Virtual Users in Postfix
• Part 5: How to Use Sagator, an Antivirus/Antispam Gateway to Protect Your Mail Server
• As you also setup locally hosted @domain.com you'd have to setup all DNS requirements for SPF, PTR, DKIM, DMARC yourself Email - Steps to ensure your site/server email doesn't end up in spam inboxes | Centmin Mod Community If you used 3rd party @domain.com, like Google App/G Suite, Zoho etc then they have GUI based control panel/instructions for setting up SPF, DKIM at their end.
• You'd then need to constantly monitor your own server's IP address for blacklisting i.e. Email Server Monitoring Service - MxToolbox and deal with each blacklist for removal of your server's IP if blacklisted. With 3rd party @domain, they would be the ones monitoring and dealing with blacklist removal