An adapter for sending emails using the SMTP protocol.

Dependencies

This adapter relies on the Mua and Mail libraries. Ensure they are added to your mix.exs file:

# mix.exs
def deps do
  [
   {:swoosh, "~> 1.3"},
   {:mua, "~> 0.2.0"},
   {:mail, "~> 0.3.0"},
   # if on OTP version below 25
   # {:castore, "~> 1.0"}
  ]
end

Configuration

For direct email sending:

# config/config.exs
config :sample, Sample.Mailer,
  adapter: Swoosh.Adapters.Mua

For sending emails via a relay:

# config/config.exs
config :sample, Sample.Mailer,
  adapter: Swoosh.Adapters.Mua,
  relay: "smtp.matrix.com",
  port: 587,
  auth: [username: "neo", password: "one"]

Define your mailer module:

# lib/sample/mailer.ex
defmodule Sample.Mailer do
  use Swoosh.Mailer, otp_app: :sample
end

For supported configuration options, please see option()

Sending Email Directly

When the relay option is omitted, the adapter sends emails directly to the recipients' mail servers. All recipients must be on the same host; otherwise, a Swoosh.Adapters.Mua.MultihostError is raised.

Ensure your application can make outgoing connections to port 25 and that your sender domain has appropriate DNS records (e.g. SPF, DKIM).

Short-lived Connections

Each deliver/2 call results in a new connection to the recipient's email server.

Sending Email via a Relay

When the relay option is set, emails are sent through the specified relay, typically requiring authentication. For example, you can use your Gmail account with an app password.

Short-lived Connections

Each deliver/2 call results in a new connection to the relay. This is less efficient than gen_smtp which reuses long-lived connections. Future versions of this adapter may address this issue.

CA Certificates

Starting with OTP 25, system cacerts are used by default for the cacerts option:

config :sample, Sample.Mailer,
  adapter: Swoosh.Adapters.Mua,
  # this happens by default
  ssl: [cacerts: :public_key.cacerts_get()]

For OTP versions below 25, CAStore.file_path/0 is used for the cacertfile option:

config :sample, Sample.Mailer,
  adapter: Swoosh.Adapters.Mua,
  # this happens by default
  ssl: [cacertfile: CAStore.file_path()]

This means that for OTP versions below 25, you need to add CAStore to your project.

You can also use custom certificates:

config :sample, Sample.Mailer,
  adapter: Swoosh.Adapters.Mua,
  ssl: [cacertfile: System.fetch_env!("MY_OWN_SMTP_CACERTFILE")]

CA Certfile Cache

When using the :cacertfile option, certificates are decoded with each new connection. To cache the decoded certificates, set :persistent_term for :mua to true:

config :mua, persistent_term: true