First of all, I would like to thank this community and the developers of Mailcow for this amazing open source project. I use it on a daily basis and I am very happy with it.
There is a problem I need to fix in order to have my service fully operative: that is, disabling the local delivery.
I use my mailcow instance as a SMTP server and as a fully mail server. Some of my clients configure their exim and postfix instances on their servers to only send through my mailcow server because I have a very good IP reputation, but they manage emails directly on their servers. Other clients instead use it as a fully featured email server, using it to send and receive emails and download them to their desktop clients.
The ones that use it as a SMTP server, I add the domain and only one mailbox, disabling sender check on that mailbox for the entire domain. The ones that use it as a fully featured email server, I add every single mailbox to the mailcow instance.
So, since I live in a rather small town and I host local business, chances are that a business I host sends an email to another business that uses my server as a SMTP server. In that case, since the mailbox will not likely exists in my mailcow instance, he won’t be able to send it, receiving an error “User unknown in virtual mailbox table”
This is a problem that actually happened once to one of my clients and I need to find a solution to it
Disabling local delivery, sending the email through the internet by searching the MX record of the domain
I read that, in order to solve this problem, it is required to have 2 instances of postfix (I suppose 2 instances of mailcow-dockerized do the trick as well).
So let’s suppose I run 2 servers with 2 instances of mailcow-dockerized on them. What steps should I follow in order to solve the problem?
Any help will be appreciated.