Sending emails is always something tricky to deal with, every ISP, antivirus, security are working on their own solution to fight scams, spam, fishing, etc. That makes difficult to have a proper SMTP server configured and trusted by all those third parties.
This post is not about what you should configure in order to your server to be trusted, but a website you can use to see what you have missed or well configured about it.
That’s being said, please check the following before give it a try:
- Ensure the public IP address used by your server to send emails is defined in the SPF record of the DNS server in charge of your domain;
- Ensure that a reverse DNS is also configured, binding this public IP address to the same name used by your SMTPS server (Hostname)
- Ensure you have configured DKIM
- Ensure your public IP address is not blacklisted
Then, you can go to this website, https://www.mail-tester.com/ . From here, you will get a temporary email address to send an email to, then by clicking on th button, it will display a very detailed amount of information about your SMTP server configuration
That’s very handy to check the basic of sending emails on Internet!