Denomailer a SMTP-client for Deno

This was forked from https://github.com/manyuanrong/deno-smtp but now is much more advanced!

Quickstart with a simple example

// please use this line and change the version to the latest version!
// import { SMTPClient } from 'https://deno.land/x/denomailer@x.x.x/mod.ts'
import { SMTPClient } from "https://deno.land/x/denomailer/mod.ts";

const client = new SMTPClient({
  connection: {
    hostname: "smtp.example.com",
    port: 465,
    tls: true,
    auth: {
      username: "example",
      password: "password",
    },
  },
});

await client.send({
  from: "me@example.com",
  to: "you@example.com",
  subject: "example",
  content: "...",
  html: "<p>...</p>",
});

await client.close();

Client

You can create a new client with const client = new SMTPClient(/* client options */).

Options

The only required option is connection.hostname but in most cases you want to set connection.,auth.

Here are the full options available:

export interface ClientOptions {
  debug?: {
    /**
     * USE WITH COUTION AS THIS WILL LOG YOUR USERDATA AND ALL MAIL CONTENT TO STDOUT!
     * @default false
     */
    log?: boolean;
    /**
     * USE WITH COUTION AS THIS WILL POSIBLY EXPOSE YOUR USERDATA AND ALL MAIL CONTENT TO ATTACKERS!
     * @default false
     */
    allowUnsecure?: boolean;
    /**
     * USE WITH COUTION AS THIS COULD INTODRUCE BUGS
     *
     * This option is mainly to allow debuging to exclude some possible problem surfaces at encoding
     * @default false
     */
    encodeLB?: boolean;
    /**
     * Disable starttls
     */
    noStartTLS?: boolean;
  };
  connection: {
    hostname: string;
    /**
     * For TLS the default port is 465 else 25.
     * @default 25 or 465
     */
    port?: number;
    /**
     * authentication data
     */
    auth?: {
      username: string;
      password: string;
    };
    /**
     * Set this to `true` to connect via SSL / TLS if set to `false` STARTTLS is used.
     * Only if `allowUnsecure` is used userdata or mail content could be exposed!
     *
     * @default false
     */
    tls?: boolean;
  };
  /**
   * Create multiple connections so you can send emails faster!
   */
  pool?: {
    /**
     * Number of Workers
     * @default 2
     */
    size?: number;
    /**
     * Time the connection has to be idle to be closed. (in ms)
     * If a value > 1h is set it will be set to 1h
     * @default 60000
     */
    timeout?: number;
  } | boolean;
  client?: {
    /**
     * There are some cases where warnings are created. These are loged by default but you can 'ignore' them or all warnings should be considered 'error'.
     *
     * @default log
     */
    warning?: "ignore" | "log" | "error";
    /**
     * List of preproccessors to
     *
     * - Filter mail
     * - BCC all mails to someone
     * - ...
     */
    preprocessors?: Preprocessor[];
  };
}

connection

You have to set the hostname and in most cases you need the auth object as (near) all SMTP-Server will require a login.

The only usecase where you might not need it is if you connect to a server with IP protection so for example only local IP are allowed so a server application can send mails without login.

Denomailer supports 3 security modes:

1. TLS
2. STARTTLS
3. unsecure

You have to specify wich to use. As unsecure you have to set extra config options in debug as it is not rcomended!

For TLS set tls: true for startTLS set tls: false (or don’t set it).

client

There are some “problems” that can be warnings or errors. With the warning option you censpecify if they should 'error' or you can 'ignore' them or 'log' them. Default is 'log'. This includes filtering invalid emails and custom preprocessors

With the preprocessors option you can add handlers that modify each mail-config. For example you can add a filter so you don’t send E-Mails to burner mails etc.

A preprocessor is of the type:

type Preprocessor = (
  mail: ResolvedSendConfig,
  client: ResolvedClientOptions,
) => ResolvedSendConfig;

It gets a preproccesed E-Mail config (ResolvedSendConfig) and the preprocessed client options (ResolvedClientOptions) and has to return a (maybe modified) E-Mail config.

pool

With a normal SMTP-Client the E-Mails are send one after the other so if you have a heavy load you might want to use more Clients at once for that we have a pool option.

You can set the amount of clients used (size) and a timeout (in ms) after that the connection is closed (timeout).

Note that for each connection we create a new Worker and the used worker syntax requires (as of deno 1.21) to use the --unstable flag. Because of that this API has to be considered unstable but we don’t expect a change! (At least for the public denomailer api internaly there might be some small changes that require specific deno versions)

When you close the connection all worker are just killed.

debug

Sometimes you have specific needs for example we require encrypted connections to send E-Mails and authentication. To enable unsecure connections set the allowUnsecure option to true depending on your needs you have to disable startTLS to get an unsecure connection use noStartTLS for this.

Note that we only use this in tests where the SMTP-Server is local and doesn’t support TLS.

If you want to get a full connection log use the log option. If you create an issue for a bug please add the full log (but remove your authentication data wich is encoded in base64).

In some cases you might get problems with Linebreaks in emails before creating an issue please try encodeLB: true that changes the encoding a little and this might solve your problem. Please create an issue if you need this option!

Examples

const client = new SMTPClient({
  connection: {
    hostname: "smtp.example.com",
    port: 465,
    tls: true,
    auth: {
      username: "example",
      password: "password",
    },
  },
  pool: {
    size: 2,
    timeout: 60000,
  },
  client: {
    warning: "log",
    preprocessors: [filterBurnerMails],
  },
  debug: {
    log: false,
    allowUnsecure: false,
    encodeLB: false,
    noStartTLS: false,
  },
});

Sending Mails

Just call client.send(/* mail config */)

Config

The config you can set:

export interface SendConfig {
  to: mailList;
  cc?: mailList;
  bcc?: mailList;
  from: string;
  date?: string;
  subject: string;
  content?: string;
  mimeContent?: Content[];
  html?: string;
  inReplyTo?: string;
  replyTo?: string;
  references?: string;
  priority?: "high" | "normal" | "low";
  attachments?: Attachment[];
  /**
   * type of mail for example `registration` or `newsletter` etc.
   * allowes preprocessors to hande different email types
   */
  internalTag?: string | symbol;
}

All of it should be clear by name except:

mimeContent

There are use cases where you want to do encoding etc. on your own. This option allowes you to specify the content of the mail.

content & html

The content should be a plain-text version of the html content you can set content to 'auto' to generate that by denomailer but in most cases you should do it on your own!

attachments

A array of attachments you can encode it as base64, text, binary. Note that base64 is converted to binary and only there for a better API. So don’t encode your binary files as base64 so denomailer can convert it back to binary.

internalTag

This can be used with preprocessors so you can give a mail a type for example 'registration', 'newsletter' etc. supports symbols and strings.

Allowed Mail Formats

A single Mail mail@example.de with a name NAME can be encoded in the following ways:

1. "name@example.de"
2. "<name@example.de>"
3. "NAME <name@example.de>"
4. {mail: "name@example.de"}
5. {mail: "name@example.de", name: "NAME"}

Multiple Mails can be an Array of the above OR a object that maps names to mails for example:

{"P1": "p1@example.de", "P2": "p2@example.de"} we call this a MailObject.

For the fields

1. from, replyTo we only allow a single mail string.
2. to, cc, bcc we allow a MailObject a Array of single Mails (you can mix formats) or a single Mail.

Examples

Example with near all options:

client.send({
  to: "abc@example.com",
  cc: [
    "abc@example.com",
    "abc <abc@example.com>",
    {
      name: "abc",
      mail: "abc@example.com",
    },
  ],
  bcc: {
    abc: "abc@example.com",
    other: "abc@example.com",
  },
  from: "me <abc@example.com>",
  replyTo: "<abc@example.com>",
  subject: "example",
  content: "auto",
  html: "<p>Hello World</p>",
  internalTag: "newsletter",
  priority: "low",
});

Other exports

We export our implementation of an quotedPrintable encoder. There might be some use cases where you need it. The api of the function is considered stable!

Stable api

All api exported by /mod.ts is considered stable. But as the pool need the --unstable flag by Deno this has to be considered unstable. But we don’t expect any breaking changes there - but if deno changes sytax etc. a new deno release can break it!

Changes to them will only be made if a new major is released.

Contribute

Feel free to contribute by:

1. creating issues for bugs and feature requests (note that you have to use the bug template to get support)
2. contribute code but keep in mind
   • for small changes you can just create a PR
   • for bigger changes please create an issue before! This will help to reduce time creating PR that are not merged.
   • if you fix a bug please add a test that fails before your fix
3. contribute tests, fix typos, …

TLS issues

When getting TLS errors make sure:

1. you use the correct port (mostly 25, 587, 465)
2. the server supports STARTTLS when using connection.tls = false
3. the server supports TLS when using connection.tls = true
4. Use the command openssl s_client -debug -starttls smtp -crlf -connect your-host.de:587 or openssl s_client -debug -crlf -connect your-host.de:587 and get the used cipher this should be a cipher with “forward secrecy”. Check the status of the cipher on https://ciphersuite.info/cs/ . If the cipher is not STRONG this is an issue with your mail provider so you have to contact them to fix it.
5. Feel free to create issues if you are ok with that share the port and host so a proper debug can be done.
6. We can only support TLS where Deno supports it and Deno uses rustls wich explicitly not implemented some “weak” ciphers.

Non SpecCompliant SMTP-Server

There are some SMTP-Server that don’t follow the spec to 100%. This can result in unexpected errors in denomailer. If this happens (for example in https://github.com/EC-Nordbund/denomailer/blob/03a66a6f9a4b5f349ea35856f5903fb45fd0cc5f/smtp.ts#L376 the server sends a 250) please create an issue. We will try and do the following:

1. Check if it is not an error in denomailer
2. Try to fix it at the SMTP-Server side (create an issue if the server is an opensource project etc.)
3. We will add a temporary workaround by changing denomailer. This will include log messages telling the developer (if the workaround is used) that denomailer used the workaround wich can be removed at any time.

Breaking changes

v0.x -> v1.0

1. Import SMTPClient not SmtpClient
2. Change the constructor options (include the options used with client.connect or client.connectTLS (add tls = true in the second case))
3. Remove client.connect and client.connectTLS calls
4. filterMail option was removed in favor of new preprocessor option
5. The client.send method did not have any breaking changes.
6. Some internal fields where removed from SMTPClient only use send and close! But in 99% of project these where not used