You will need to create a group in WGM called mycompany and add the members you want to send email to. The normal email address would be This e-mail address is being protected from spambots. You need JavaScript enabled to view it

In Server admin -> Mail -> Settings -> Mailing Lists mark the box "Enable Server Groups Mailing Lists" leave the "Update recipient mailing list every 10 minutes". 

Using the web interface create a wiki called mycompanylist and enable 'mailing lists' under setting. Any user can be the owner of tis wiki. You not actually have to use the wiki: Just set some settings. 

Using the web interface, under Settings -> Services enable "mailing list" 

Using the web interface, under Settings -> Permissions enable "This wiki can be read and edited by only the following users and groups" and select the group you created in the work group manager: mycompany by typing the first 3 charters in the "type a user or group here" box. Once it finds it, press enter. You can make this group "read only" It should not matter. 

Now you can email to the group by sending a email to wiki using the email address:

mycompanylist-wiki@mycompanyurl.com . 

The "-wiki" is not very elegant. So I like to create an user in WGM named everybody which forwards the email to mycompanylist-wiki@mycompanyurl.com . It is easer to remember and if you start to get spam on that email address, you can easily create a new user. People can now send email to 

everybody@mycompanyurl.com

Test and you are done. You can now add and remove the members of the email list in WGM mycompany list. 

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We assume that all servers are running on the same machine. (Standard Apple configuration).