By default, this playbook sets up an [Exim](https://www.exim.org/) relay SMTP mailer service (powered by [exim-relay](https://github.com/devture/exim-relay) and the [ansible-role-exim-relay](https://github.com/mother-of-all-self-hosting/ansible-role-exim-relay) Ansible role), through which all Matrix services send emails.
**With the default setting, exim-relay attempts to deliver emails directly with the address `matrix@matrix.example.com`**, as specified by the `exim_relay_sender_address` playbook variable. See below if you want to configure the playbook to relay email through another SMTP server.
The Ansible role for exim-relay is developed and maintained by [the MASH (mother-of-all-self-hosting) project](https://github.com/mother-of-all-self-hosting/ansible-role-exim-relay). For details about configuring exim-relay, you can check them via:
- 🌐 [the role's documentation at the MASH project](https://github.com/mother-of-all-self-hosting/ansible-role-exim-relay/blob/main/docs/configuring-exim-relay.md) online
- 📁 `roles/galaxy/exim_relay/docs/configuring-exim-relay.md` locally, if you have [fetched the Ansible roles](installing.md#update-ansible-roles)
No matter whether you send email directly (the default) or you relay email through another host, you'll probably need to allow outgoing traffic for TCP ports 25/587 (depending on configuration).
Docker automatically opens these ports in the server's firewall, so you likely don't need to do anything. If you use another firewall in front of the server, you may need to adjust it.
**On some cloud providers such as Google Cloud, [port 25 is always blocked](https://cloud.google.com/compute/docs/tutorials/sending-mail/), so sending email directly from your server is not possible.** In this case, you will need to relay email through another SMTP server.
For details about configuration, refer [this section](https://github.com/mother-of-all-self-hosting/ansible-role-exim-relay/blob/main/docs/configuring-exim-relay.md#relaying-email-through-another-smtp-server) on the role's document.
See [this section](https://github.com/mother-of-all-self-hosting/ansible-role-exim-relay/blob/main/docs/configuring-exim-relay.md#troubleshooting) on the role's documentation for details.
