I will admit, setting up email in such a way that emails are delivered to recipient's inboxes is difficult.
I'm going to assume that you are currently setting up email by yourself, with your host, or your server(s) are the ones sending the emails, rather than something like Mailgun.
You'll need to ensure that if you are using something like "mail.yourdomain.com" as where your emails are being sent from.
For "mail.yourdomain.com", You'll want to make sure that you setup the following records with your server DNS: SPF, DKIM, and DMARC records.
If you have a control panel like cPanel installed, this is a trivial exercise as it's just a matter of going into your cPanel account and setting up the SPF and DKIM records through the "Email Deliverability" section.
For DMARC records, you'll want to go into the DNS Zone Manager and create a new DMARC zone.
In this DMARC record, I would recommend using Quarantine as the policy for each option, then setting an email for any failed domain checks. I would recommend setting up an email account specifically for these domain reports just so they don't clog your mailbox.
Additionally, I would recommend having a dedicated IP address for your mail server, to help eliminate the possibility of others getting your mail server IP blacklisted.
Finally, I would check through all the blocklists to see if your IP shows up on any of them. If ANY blocklist shows your IP as an offender, then you'll want to reach out to the block list and submit a request to have it removed from the blocklist. This will help your reputation overall to not have email deliverability issues.
