Posted for rudydehaas: hi: I posted this as a comment on the "Perfect Server: Debian 10.." article and got a response asking that I post it here. So... I did a new, from bear metal, install of Debian 10 on a Dell Xeon. DNS and the reverse ptr are correct for this new machine as wadocan.net . Then, being too lazy to look it all up for myself I used the instructions in the perfect server article to load everything. When finished, everything worked except email - localhost/webmail - that reported an smtp access error. So I re-installed (from scratch) and then followed the instructions again except that I did not install things like webalizer, phpmyadmin, and ISPconfig inself. Same error. So I installed dovecot and brought up thunderbird. Thunderbird reported that it would not connect because the certificate was self-signed. So I re-installed certbot using snapd and pushed certbot keys into the postfix /etc../live/wadocan.net/ directory. Now thunderbird will send mail but the system will not accept (or store sent) mail. The error is: Final-Recipient: rfc822; <a href="mailto:[email protected]">[email protected]</a> Action: failed Status: 5.7.1 Remote-MTA: dns; wadocan.net. (18.104.22.168, the server for the domain wadocan.net.) Diagnostic-Code: smtp; 554 5.7.1 <a href="mailto:[email protected]"><[email protected]></a>: Relay access denied Last-Attempt-Date: Fri, 09 Oct 2020 11:46:28 -0700 (PDT) Roundcube, however, will not send mail. It's response is: SMTP Error (504): Failed to add recipient "[email protected]" (5.5.2 <localhost>: Helo command rejected: need fully-qualified hostname). At this point I have no idea whether the problem lies in the postfix or dovecot set-ups.. ? or somewhere else.