Emails sent from Post Affiliate Pro are sometimes delivered only to certain email servers, while others may not receive them at all. Additionally, these emails are often marked as spam.
To diagnose this issue, review your email (SMTP) server logs. If you encounter a log entry similar to the following:
May 9 13:01:00 example postfix/smtp[12722]: 71F4110179: to=<support@qualityunit.com>, relay=qualityunit.com[50.28.21.67]:25, delay=2.3, delays=0.53/0.01/1.6/0.15, dsn=5.0.0, status=bounced (host qualityunit.com[50.28.21.67] said: 550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1) (in reply to MAIL FROM command))
This likely indicates that your email server's host name is incorrectly configured.
Ensure that the host name specified in your SMTP server configuration contains the fully qualified domain name (FQDN) of the SMTP client. In cases where the SMTP client system does not have a meaningful domain name, the client should send an address literal instead.