I installed Mailcow on my.host.com (it works fine)
I added a second domain: second.domain
First using: mail.second.domain on DNS (MX, CNAME, SRV)
Now I’m using my.host.com on DNS (MX, CNAME, SRV)

ERROR trying port: 110
[AUTH] Plaintext authentication disallowed on non-secure (SSL/TLS) connections.

ERROR trying port: 143
Missing +OK response upon connecting to the server: * OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ STARTTLS LOGINDISABLED] Dovecot ready.

ERROR trying port: 993
Connection timed out: There may be a problem with the settings you added. Please contact your other email provider to verify the correct server name and port.

NGINX my.host.com.conf (I don’t have nginx conf for mail.second.domain)
`
server {
listen 80 default_server;
listen [::]:80 default_server;
server_name my.host.com autodiscover.* autoconfig.;
return 301 https://$host$request_uri;
}
server {
listen 443 ssl http2;
listen [::]:443 ssl http2;
server_name my.host.com autodiscover. autoconfig.*;

ssl_certificate /etc/mailcow-dockerized/data/assets/ssl/cert.pem;
ssl_certificate_key /etc/mailcow-dockerized/data/assets/ssl/key.pem;
ssl_session_timeout 1d;
ssl_session_cache shared:SSL:50m;
ssl_session_tickets off;

See https://ssl-config.mozilla.org/#server=nginx for the latest ssl settings recommendations

An example config is given below

ssl_protocols TLSv1.2;
ssl_ciphers HIGH:!aNULL:!MD5:!SHA1:!kRSA;
ssl_prefer_server_ciphers off;

location /Microsoft-Server-ActiveSync {
proxy_pass http://127.0.0.1:7780/Microsoft-Server-ActiveSync;
proxy_set_header Host $http_host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_connect_timeout 75;
proxy_send_timeout 3650;
proxy_read_timeout 3650;
proxy_buffers 64 512k; # Needed since the 2022-04 Update for SOGo
client_body_buffer_size 512k;
client_max_body_size 0;
}

location / {
proxy_pass http://127.0.0.1:7780/;
proxy_set_header Host $http_host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
client_max_body_size 0;

The following Proxy Buffers has to be set if you want to use SOGo after the 2022-04 (April 2022) Update

Otherwise a Login will fail like this: mailcow/mailcow-dockerized4537

proxy_buffer_size 128k;
proxy_buffers 64 512k;
proxy_busy_buffers_size 512k;
}
}
`

mailcow.conf
`
HTTP_PORT=7780
HTTP_BIND=127.0.0.1

HTTPS_PORT=7743
HTTPS_BIND=127.0.0.1

ADDITIONAL_SAN=mail.second.domain

ADDITIONAL_SERVER_NAMES=mail.second.domain

ENABLE_SSL_SNI=y
`

OPEN PORTS on UFW
80,443,22,25,110,143,465,587,993,995,4190,7780,7743