To setup you Mail server properly, please make sure your:
must not match any domain that is being used on the system. Example, if you have a domain called domain.com and you want to receive mail on firstname.lastname@example.org, you must *not* set your hostname to domain.com. We recommend using host.DOMAIN.TLD instead. You must make sure that you add the A record for host.DOMAIN.TLD so that it resolves.
hostname must be in the /etc/virtual/domains file.
hostname must *not* be in the /etc/virtual/domainowners file.
hostname must resolve. If not, add the required A records to the dns
zone such that it does.
The directory /etc/virtual/hostname must exist. (For example: /etc/virtual/host.DOMAIN.TLD). It must not contain any files.
Any domains that you want to use for email (For example: DOMAIN.TLD) must be in both the /etc/virtual/domains file and the /etc/virtual/domainowners file. The directory /etc/virtual/DOMAIN.TLD must exist, and the files /etc/virtual/DOMAIN.TLD/passwd and /etc/virtual/DOMAIN.TLD/aliases exist as well.
Ensure your hostname does not contain any upper case letters.
Make sure that your main server IP
has a reverse lookup on it.