Email is a standard way of communication these days and creating a reliable email delivery can be tricky. Most of times your email get into Junks or treated as a spam. If you are setting your own email server there are some thing you should aware of for reliable email delivery.
Make sure mail server is not configured as a Open Relay.
If your server is configured as a open relay any one can send emails through your email server and can spam to any one. Your email server soon will be blocked or mark as a spammer. You can check if your SMTP server is configured as open relay at http://mstoolbox.com.
Setting reverse lookup zone
It’s not necessary to create a reverse lookup for your domain, but it’s always a good practice to create it.
Check if your server is blacklisted.
It’s possible that recently your severs sent too many spams, or you got an IP address which used to a spammer. Before starting anything make sure your IP is not blacklisted or if it’s blacklisted request the ISP to remove it. You can check where your IP is blacklisted at http://mstoolbox.com.
Now a days most of email providers like Gmail, Yahoo, Hotmail or AOL check for authority of emails and for this you need to configure these things in your email server.
SPF records: SPF(Sender Policy Framework) is an DNS record which describe which IP’s can send email on domain’s behalf. When email is arrives at email servers, servers check domains SPF record if this ip is permitted to send mail on this domain’s behalf. If you don’t aware of what is SPF and how to create is you can get to these link and try by your self.
Learn SPF Record: http://www.openspf.org/SPF_Record_Syntax
Create SPF Record: http://www.spfwizard.net/
Validate SPF Record: http://www.kitterman.com/spf/validate.html
DKIM: DKIM(DomainKeys Identified Mail) provides a method for validating a domain name identity that is associated with a message through crystallographic authentication. DKIM is an public and private key combination. Your Private key is stored as an TXT record on DNS. When MTA send an email it signed it with a public key and when receiving MTA accept this email it get the private key from DNS and verify the authority of mail server.
DKIM for Postfix: install-and-configure-dkim-with-postfix
DMARC: DMARC(Domain-based Message Authentication, Reporting & Conformance) is an email authentication protocol widely deploy with SPF and DKIM. It’s allows senders and receivers to improve and monitor protection of the domain from fraudulent email.
Create DMARC: https://app.agari.com/dmarc/record_creator
Create DMARC: https://www.unlocktheinbox.com/dmarcwizard/
If you follow all this there is a 99% guarantee of inboxing. Apart for all this some time because of your email content it goes to spam. Always check your email integrity. There is a good way to find your your email score at https://www.mail-tester.com/
If you are also having the inbox send a test email to these id and get result in mailbox.