When your emails aren’t being received, it could be that they are being blocked by a spam filter. To what extent and for what reasons can be tested at https://www.mail-tester.com/
The website shows an email address where you can send your email, leave this page open. Copy the email address that’s being provided to your email client and send a real mailing (test emails don’t properly reflect the issue of emails not being received).
After you have send the email return to the page, where you click ‘Then check your score’. You’ll then see a list with reasons why your emails aren’t being received and you’ll get some tips on how to optimise your emails.