feat!: Email support using lettre #419

ElijahAhianyo · 2025-12-01T17:16:30Z

This is a continuation of #250

Initial commit of email.rs using lettre Initial commit of Add email support using lettre crate Added the message printout if debug mode is enabled Added a test and deferred the extra headers and attachment features. Added tests for config and send_email(ignore).

…/cot into feat-add-email-support

…ded to improve test coverage.

…elp.

Copilot

Pull request overview

This PR adds comprehensive email support to the Cot framework using the lettre library, providing both console (development) and SMTP (production) transport backends for sending emails.

Key Changes:

Implements high-level Email API with EmailMessage builder pattern for constructing and sending emails
Adds console and SMTP transport backends with pluggable architecture via Transport trait
Integrates email service into the request context and project configuration system

Reviewed changes

Copilot reviewed 26 out of 27 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
`examples/send-email/`	Complete example application demonstrating email functionality with HTML form and status feedback
`cot/src/email/`	Core email module with message building, transport abstraction, and backend implementations
`cot/src/config.rs`	Email configuration structures supporting console and SMTP transports with URL-based config
`cot/src/request.rs`	Request extension trait additions to access email service
`cot/src/project.rs`	Email service initialization and integration into project bootstrap lifecycle
`cot/Cargo.toml`	New `email` feature flag and `lettre` dependency
`deny.toml`	Apache-2.0 WITH LLVM-exception license allowance for new dependencies
`cot-cli/src/project_template/`	Default email configuration in project templates
`.github/workflows/rust.yml`	CI toolchain version updates
`.cargo/config.toml`	Windows linker configuration for faster builds

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cot/src/email.rs

examples/send-email/templates/index.html

cot/src/email/transport/smtp.rs

cot/src/config.rs

examples/send-email/src/main.rs

cot/src/email/transport.rs

m4tx

That's a really nice piece of work! I'll need to have another look at the actual email logic in the PR, but this overall looks decent. Please make sure to have a look at the Copilot review as well - it has found a few nitpicks.

.cargo/config.toml

cot-cli/src/project_template/.cargo/config.toml

cot/src/project.rs

cot/src/request.rs

examples/send-email/Cargo.toml

examples/send-email/src/main.rs

cot/src/email.rs

cot/src/email/transport/console.rs

This makes the API more ergonomic, as `Arc` should really just be an implementation detail, rather than something exposed to the user. This is a followup to the discussion here: #419 (comment)

cot/Cargo.toml

m4tx

I think this is the last batch of comments - overall, it's really, really good, but I still have a few concerns. Nothing fundamental, mostly nitpicks!

cot/src/email.rs

m4tx · 2026-01-05T16:31:05Z

cot/src/email.rs

+    ///     .build()?;
+    ///  email.send(message).await?;
+    /// # Ok(())
+    /// }


m4tx · 2026-01-05T16:31:10Z

cot/src/email.rs

+    ///     .build()?;
+    ///  email.send_multiple(&[message1, message2]).await?;
+    /// # Ok(())
+    /// }


m4tx · 2026-01-05T16:34:19Z

cot/src/email/transport/console.rs

+/// let console_transport = Console::new();
+/// ```
+#[derive(Debug, Clone, Copy)]
+pub struct Console;


I think we should add #[non_exhaustive] to the structure. I'm not sure if we'll ever add any configuration options to this transport, but if we do, we will be able to do this in an API-compatible way, unlike now.

m4tx · 2026-01-05T16:36:08Z

cot/src/email/transport.rs

+pub enum TransportError {
+    /// The underlying transport backend returned an error.
+    #[error("{ERROR_PREFIX} transport error: {0}")]
+    Backend(String),


Shouldn't we have Box<dyn StdError + Send + Sync + 'static> here so that we don't lose the original error? Is there any reason to only keep String here?

cot/src/config.rs

m4tx · 2026-01-05T16:53:47Z

cot/src/email.rs

+    type Error = EmailMessageError;
+
+    fn try_from(message: EmailMessage) -> Result<Self, Self::Error> {
+        let from_mailbox = message


Why can't we just add server_email: Option<String> to EmailConfig? What do you mean "there's no nice way to do that"?

m4tx · 2026-01-05T16:57:15Z

cot/src/email/transport/smtp.rs

+/// The default is `Plain`.
+#[derive(Debug, Default, Copy, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum Mechanism {


Let's add #[non_exhaustive] here so that when we add new auth mechanisms, it won't be a breaking change.

m4tx · 2026-01-05T17:04:52Z

cot/src/email.rs

+
+impl_into_cot_error!(EmailMessageError);
+
+impl TryFrom<EmailMessage> for Message {


Can we move this to smtp.rs and make it a separate function, rather than impl TryFrom<..> for Message? I ask for several reasons:

This is the file that contains a public API we expose to the users; I don't think that code that's specific to any transport implementation (in this case, smtp) belongs here.

This sneakily exposes lettre in our public API. If we ever change lettre to any other library, or even bump the lettre's version, this will be a hidden breaking change for our users (even though probably nobody will actually try to use this).

If we ever add more transports supported by lettre (such as the sendmail transport), we can move this code to some shared module, but I still don't think this belongs here.

Yeah, I agree with this

m4tx · 2026-01-05T17:06:27Z

cot/src/config.rs

+#[cfg(feature = "email")]
+#[derive(Debug, Default, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(tag = "type", rename_all = "snake_case")]
+pub enum EmailTransportTypeConfig {


We should add #[non_exhaustive] here, as it's highly likely we'll add new transport types in the future.

Co-authored-by: Mateusz Maćkowski <mateusz@mackowski.org>

trkelly23 and others added 27 commits March 15, 2025 14:12

Initial commit of email.rs using lettre

1d2849e

Initial commit of Add email support using lettre crate

252cebe

Added the message printout if debug mode is enabled

fc1fb9f

Added a test and deferred the extra headers and attachment features.

d64980f

Added tests for config and send_email(ignore).

4edd6d0

Fixed the email example and removed minor version from cargo.

dbbf50f

chore(pre-commit.ci): auto fixes from pre-commit hooks

0587340

Merge branch 'feat-add-email-support' of https://github.com/trkelly23…

84eb659

…/cot into feat-add-email-support

chore(pre-commit.ci): auto fixes from pre-commit hooks

c964e45

Implemented a trait impl for the EmailBackend

a13552e

chore(pre-commit.ci): auto fixes from pre-commit hooks

6ac6e92

Refactor to insure multiple email backends could be added. Mocking ad…

d7ac14a

…ded to improve test coverage.

Pushing lock since there seems to be a conflict

4ee5c6a

Merge branch 'master' into feat-add-email-support

49775cd

chore(pre-commit.ci): auto fixes from pre-commit hooks

553c2e9

Adding the reworked smtp implementation and NOT working example for h…

cb8093a

…elp.

chore: cargo fmt

749ef05

fix bootstrapper

3a042af

chore: merge master

84c111d

chore(pre-commit.ci): auto fixes from pre-commit hooks

ea8e2e0

Merge branch 'master' into feat-add-email-support

fa4f337

Merge branch 'master' into feat-add-email-support

6cc9cb6

Tested send-email example and cleaned up code

83652f1

Merge branch 'master' into feat-add-email-support

33e49c2

Merge remote-tracking branch 'upstream/master' into trkelly23-fix-email

587444d

add cargo lock

bd0f3be

github-actions bot added the C-lib Crate: cot (main library crate) label Dec 1, 2025

chore(pre-commit.ci): auto fixes from pre-commit hooks

88eaecc

ElijahAhianyo mentioned this pull request Dec 1, 2025

feat: email support using lettre #250

Open

remove profile test

b5da565

m4tx requested a review from Copilot December 24, 2025 00:02

Copilot started reviewing on behalf of m4tx December 24, 2025 00:02 View session

Copilot AI reviewed Dec 24, 2025

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m4tx requested changes Dec 24, 2025

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m4tx mentioned this pull request Dec 24, 2025

refactor!: use Arc internally in Database #432

Merged

m4tx added 2 commits December 24, 2025 13:23

Merge branch 'master' into elijah/trkelly23-fix-email

ab7f4e5

bump askama

9019d55

m4tx reviewed Dec 24, 2025

View reviewed changes

cot/Cargo.toml Outdated Show resolved Hide resolved

ElijahAhianyo and others added 15 commits December 25, 2025 12:21

address most of the PR comments

4fbdf39

use tokio-rustls

71c516e

using tokio-rustls needs ring feature

d550869

whitelist licenses required by lettre

9e539ec

fix clause

0e44378

not sure what happened there

2420300

apparently we need this

79d5d24

more whitelist

8bc83bd

test excluding examples

e97aa58

Merge branch 'master' into elijah/trkelly23-fix-email

ca5263e

update workflow

90f913a

Pin the idna version to ^1.1

854b38c

Update Cargo.lock

9ca90bd

also pin chumsky

71e3c44

remove the exclude examples flag from cargo hack

a71db21

ElijahAhianyo requested a review from m4tx December 31, 2025 15:48

ElijahAhianyo added 2 commits January 3, 2026 14:22

introduce indirection

73c83e4

Merge branch 'master' into elijah/trkelly23-fix-email

bd2979f

m4tx requested changes Jan 5, 2026

View reviewed changes

Apply suggestions from code review

8d84c7b

Co-authored-by: Mateusz Maćkowski <mateusz@mackowski.org>


		impl_into_cot_error!(EmailMessageError);

		impl TryFrom<EmailMessage> for Message {

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feat!: Email support using lettre #419

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feat!: Email support using lettre #419

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ElijahAhianyo commented Dec 1, 2025

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