MailCatcher is a nice tool to catch generated E-Mails. However, the default installation is meant for standard localhost set up. When usign Vagrant, Docker or both for isolating different projects it would be nice to use a single installation of MailCatcher on your development machine. This example covers a set up for PHP projects. Usually, when setting up MailCatcher with PHP it is required to configure sendmail_path in your php.ini like this:

sendmail_path = /usr/bin/env catchmail -f some@from.address

The drawback with this approach is, that catchmail is coming from the MailCatcher installation and therefore it would be necessary to install MailCatcher on the virtual machine provided by Vagrant or inside the corresponding docker container. I was however looking for a solution to avoid this overhead and use a single installation on my host system. It is a little bit tricky because the default sendmail is not able to forward mails to another host/port without a lot of configuration overhead. With mini_sendmail however, I found a working solution with following php.ini configuration:

sendmail_path = /usr/bin/mini_sendmail -s192.168.56.1 -p1025 -t -i

From inside a virtual machine, 192.168.56.1 would be the address of the host system and port 1025 the port where CatchMail is listening. It is also required to define the address where CatchMail should listen because the default value is localhost and a connection would not be possible. This is why CatchMail needs to be started with the argument smtp-ip:

catchmail --smtp-ip 192.168.0.1

Inside Docker

However, I had one issue using mini_sendmail inside a docker container. It failed with:

can't determine username

I currently don’t know the reason for this. It must have something to do with the glibc method getLogin() used by mini_sendmail which was not available inside my docker container for whatever reason. However, a dirty workaround was to change the line

username = getlogin();

to

username = "root";

and recompile mini_sendmail which did the trick.