"Restrict Mailcow to Only Send/Receive Emails with a Specific Domain"

NikhilYadav2000

I have a domain abc.in, which is hosted on Mailcow, and I want to restrict its email communication only to abc.com. This means:

abc.in should only be able to send and receive emails from abc.com.
Emails to and from any other domains (Gmail, Yahoo, etc.) should be completely blocked.

What is the best way to achieve this in Mailcow?

ETNyx

Hello, I assume abc.com is trusted server, so if you need pure p2p system Mailcow looks like overkill, while using all fancy antispam things and so,..

Anyway in theory for outgoing mails i would modified transport_map something like

* discard:
abc.com smtp:[abc.com]

And for outgoing i would used smtpd_client_restrictions like

smtpd_client_restrictions = permit_mynetworks, check_client_access hash:/etc/postfix/allowed_clients, reject

and allowed_clients

abc.com OK

If you are lucky, you could be able to setup this over MC UI in System -> Configuration find Routing, Global filter maps and/or Forwarding Hosts

NikhilYadav2000

ETNyx Could you please help me with how to do this using the Mailcow UI?

ETNyx

Sorry, nope, for example I do not fully understand “Global filter maps” and how they are wired into inner function of MC. I would suggest to use official support since you want something that is not in regular scope, by my understanding.

NikhilYadav2000

ETNyx Thank you for your help! I asked because doing it this way wasn’t working.

Discarded:
abc.com smtp:[abc.com]

For outgoing, I used smtpd_client_restrictions like this:

smtpd_client_restrictions = permit_mynetworks, check_client_access hash:/etc/postfix/allowed_clients, reject

And in allowed_clients:

abc.com OK

ETNyx

Postfix can be hard to configure, that is why I suggest to use professional help. I would guess that you made this config in extra.conf right? Are you sure it’s not overridden? For example on per server/service configuration, if I remember it right MC does it on multiple occasion,..

NikhilYadav2000

is there any other way to achieve this?

NikhilYadav2000

If you want a Mailcow-hosted domain (e.g., abc.in) to only send and receive emails to/from one specific domain (e.g., abc.com) and block all other domains (Gmail, Yahoo, etc.), here’s how to do it:

✅ Steps to configure:
Edit /opt/mailcow-dockerized/data/conf/postfix/allow_mailcow_local.regexp
Add this single-line regex to allow only the desired domains:

/^(.*@abc.com|.*@abc.in)$/ OK

🔸 Important: Mailcow reads this file as a single regex line. Writing multiple lines like:

abc.com OK  
abc.in OK

won’t work.

Edit /opt/mailcow-dockerized/data/conf/postfix/header_checks.regexp
Add this to block incoming mail from other domains like Gmail or Yahoo:

/^From:.*@(gmail\.com|yahoo\.com)/ REJECT "Emails from Gmail and Yahoo are not allowed."

`Edit main.cf and update the following sections:

smtpd_sender_restrictions =
** #COMMENT EVERYTHING ELSE HERE**
check_sender_access regexp:/opt/postfix/conf/allow_mailcow_local.regexp,
reject
 
smtpd_recipient_restrictions =
** #COMMENT EVERYTHING ELSE HERE**
check_recipient_access regexp:/opt/postfix/conf/allow_mailcow_local.regexp,
reject
 
header_checks = regexp:/opt/postfix/conf/header_checks.regexp

Restart Mailcow / Postfix to apply the changes.