Redmine

This plugin enables you to configure a list of email domains that can be specified in Redmine user profiles.
To do this, go to Administration > Plugins and click Configure.

Note that the configured settings will be applied only if you select the Enabled check box.

To add a domain to Redmine whitelist, click Add domain and type the domain in the corresponding field. You can add as many domains as you need. To remove a domain from the list, click Remove domain.

In the Message if domain is not in whitelist field, you can specify a custom text to be displayed if a user tries to create a new account and enters an email that is not allowed.

In the Mail banner message field, you can add a text prompt that will be displayed below the Email field on the New user page.

The initial author of this plugin is Vladimir Kiselev.

To install the plugin
Download the .ZIP archive, extract files and copy the plugin directory into #{REDMINE_ROOT}/plugins.
Or
Change you current directory to your Redmine root directory:

cd {REDMINE_ROOT}

git clone https://github.com/Undev/redmine_profile_email_domain_whitelist.git plugins/redmine_profile_email_domain_whitelist

2. Install the required gems:

bundle install

3. Restart Redmine.