Been churning away at this for over 7 hours. Numerous config changes/testing, service statuses/restarts, server rebuilds/restarts. I've been through every forum thread I can find. Fresh VPS server pre-configured by GoDaddy. Ubuntu 16.04 w/ ISPConfig 3 I'm 99.9% sure my MX record is set up properly: A[mail]->serverIP, MX[@]->mail.mydomain.com Prep: Brand new server build ISPConfig ServerConfig to add the GoDaddy SMTP Relay to the Relayhost setting, so that I can send outbound mail. ISPConfig EmailDomains to add mydomain.com as a mail domain. ISPConfig EmailMailboxes to add [email protected] as an email inbox. Sidenote: for whatever reason, at this point, I can't send emails until I restart the server. Not sure if this is a GoDaddy/ISPConfig bug or what. Anyway, it seems to be a non-issue after restarting, and I'm able to send outbound emails from [email protected] to [email protected] My problem is that no matter what I do, I can't get inbound mail to deliver. I can't get mail to deliver from [email protected] to [email protected], from [email protected] to [email protected], or from [email protected] to [email protected] Normally I'd expect to receive a "Mail Delivery Failure" response in Gmail after sending a failed/undeliverable email. That doesn't happen. Everything seems to indicate the message was delivered, except that it never shows up in the mailbox. I see no errors or warnings in mail.log while sending these messages. Most obviously, I see no status in mail.log that indicates the server is receiving/handling the inbound delivery at all. How can I go about troubleshooting this? Any help is appreciated. Thanks in advance.