Новый почтовый сервер не может послать электронные письма, только получает
Посмотрите на man sshd и поиск AUTHORIZED_KEYS FILE FORMAT
То, что Вы хотите сделать, создают пару "открытый/закрытый ключ" и вставляют открытый ключ ~/.ssh/authorized_keys файл как нормальный. Затем отредактируйте authorized_keys файл для добавления строки:
управляйте = "/bin/false", no-agent-forwarding, без имуществ, no-user-rc, no-X11-forwarding, permitopen = "127.0.0.1:80"
Это закончит тем, что смотрело отчасти как:
command="/bin/false",no-agent-forwarding,no-pty,no-user-rc,no-X11-forwarding,permitopen="127.0.0.1:80" ssh-dss AAAAC3...51R==
Вы хотели бы изменить аргумент 'permitopen' и возможно изменить некоторые из других настроек, но я думаю, что это - в основном он.
From your main.cf:
default_transport (default: smtp) You used: default_transport = error
The default mail delivery transport and next-hop destination for destinations that do not match $mydestination, $inet_interfaces, $proxy_interfaces, $virtual_alias_domains, $virtual_mailbox_domains, or $relay_domains
Well, that does it. Remove this line. You want to use SMTP to send out email that isn't for your domain. Right now, you've forced yourself to only perform local delivery (any mail that is supposed to go anywhere outside of that machine will not be accepted). That's why you can receive mail, but nothing that isn't accepted by that host is forwarded.
relayhost (default: empty) You used: relayhost = $mydomain
The next-hop destination of non-local mail; overrides non-local domains in recipient addresses. This information is overruled with relay_transport...
This definitely affects things. Unless you have a different SMTP server listening on enti.centropaghe.it that you want all mail to go through, your mail is again going nowhere. You probably should remove this line.
relay_transport (default: relay) You used: relay_transport = error
The default mail delivery transport and next-hop destination for remote delivery to domains listed with $relay_domains. In order of decreasing precedence, the nexthop destination is taken from $relay_transport, $sender_dependent_relayhost_maps, $relayhost, or from the recipient domain
I see no $relay_domains, so I suggest removing this.
Update
Ah, horse of a different color. This line below says who is allowed to relay. Your error message is coming from a host beginning with 213.178. Since there is no entry for it and you have other form of authentication for relaying, it is denied. Perhaps you want to add an entry covering your assigned network range?
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 192.168.1.0/24
Let me know how that works out for you.