Email Postfix problems

Who's your web host ? some web hosts block outgoing smtp email ports until you contact them to request unblocking i.e. Vultr does this and require you to provide ID verification to unblock you.

As to email delivery, ensure SPF/TXT DNS records are setup properly too.

Centmin Mod is provide as is, so short of scripted related bugs or issues, any further optimisation to the web stack components - nginx, php-fpm, mariadb mysql, csf firewall etc or web app specific configurations are left to the Centmin Mod user to deal with. So I do not provide any free support for such things as SPF/TXT and DNS records. You're best to ask your web host and/or domain registrar and follow below instructions and check out thread at Email - error in PTR, mails goes to gmail Spam folder

However, Centmin Mod users are free to help each other out and ask questions or give answers on this community forum. My hopes are that this community forum evolves so that more veteran long time Centmin Mod users help new Centmin Mod users out

Generally, to insure email sent from your Centmin Mod LEMP server's postfix MTA doesn't end up in email recipient's spam box, you need to at least have proper DNS level configurations for

1. SPF / TXT record setup in DNS with your DNS provider. SPF / TXT record is a DNS text record so how you add it will depend on your DNS provider. Some info here, here and here. Also SPF guides from some Domain/DNS providers such as Namecheap.com, Godaddy.com, and check out SPF Wizard - SPF Generator DNS tool. Ensure both your site's domain name and server's main hostname from Getting Started Guide step 1 have valid SPF TXT records
2. Reverse PTR record, you will need to ask your web host for that. Some web hosts and VPS providers use SolusVM control panels and allow you to setup a PTR record yourself. Basically it points your server's IP to your domain name. So when a reverse lookup on the IP is made, it resolves to your domain name. For instance the PTR record for this forum's IP = 173.230.147.144 resolves to community.centminmod.com when you do a reverse IP lookup at IP Address Lookup (IPv4 & IPv6). I use Linode.com for my forum hosting and their control panel has the relevant PTR record support for reverse dns.

IP Blacklist Check

Also check if your web site and server IP addresses are in spam blacklists using services like:

• Email Blacklist Check - See if your server is blacklisted
• Blacklist Check
• Blacklist Lookup | Sender Score | Return Path

Straight from Amazon SES best practices guide, you should also check the URL links that you use in your emails against blacklists as well, because some ISPs will block email with blacklisted links. URIBL.com and SURBL.org are two very useful sites that you can use to determine whether your links are blacklisted. Remember to check any links provided to you by a third party or any link shorteners, which obfuscate your domain or links.

Transactional Email Providers

For forum, CMS etc outbound email and best email deliverability, best to use a 3rd party SMTP transactional email provider. Discussion of provider options can be read at Email - Mandrill users will be required to have a paid monthly MailChimp account. I use Amazon SES for this forum's emails.

SPF Setup Guides

• Create a SPF record for your server - mail-tester.com

SPF Wizards

You can use SPF wizards to try and get the correct settings

• SPF Wizard - SPF Generator DNS tool <-- probably best one
• easySPF: an Ajax enabled SPF Wizard
• Create SPF records with MailRadar SPF Wizard
• SPF Wizard
• xNode - SPF Record Creator

SPF Testing Tools

• Also test validity of your SPF txt record at SPF Query Tool
• whatsmydns.net - select TXT record dropdown and enter domain as well as server's main hostname from Getting Started Guide step 1
• solvedns.com - select TXT record dropdown and enter domain as well as server's main hostname from Getting Started Guide step 1