Configuring AWS Lambda for Amazon WorkMail - Amazon WorkMail

Configuring AWS Lambda for Amazon WorkMail

Use the Run Lambda action in inbound and outbound email flow rules to pass email messages that match the rules to an AWS Lambda function for processing.

Choose from the following configurations for a Run Lambda action in Amazon WorkMail.

Synchronous Run Lambda configuration

Email messages that match the flow rule are passed to a Lambda function for processing before they are sent or delivered. Use this configuration to modify email content, and to control inbound or outbound email flow for use cases such as blocking delivery of sensitive email messages, removing attachment, adding disclaimers, and so on.

Asynchronous Run Lambda configuration

Email messages that match the flow rule are passed to a Lambda function for processing while they are sent or delivered. This configuration does not affect email delivery and is used for tasks such as collecting metrics for inbound or outbound email messages.

Whether you choose synchronous or asynchronous configuration, the event object passed to your Lambda function contains metadata for the inbound or outbound email event. You can also use the message ID in the metadata to access the full content of the email message. For more information, see Retrieving message content with AWS Lambda. For more information about email events, see Lambda event data.

For more information about inbound and outbound email flow rules, see Managing email flows. For more information about Lambda, see the AWS Lambda Developer Guide.

Note

Currently, Lambda email flow rules reference only Lambda functions in the same AWS Region and AWS account as the Amazon WorkMail organization being configured.

Getting started with AWS Lambda for Amazon WorkMail

To start using AWS Lambda with Amazon WorkMail, we recommend deploying the WorkMail Hello World Lambda function from the AWS Serverless Application Repository to your account. The function has all the necessary resources, and the permissions configured for you. For more examples, see the amazon-workmail-lambda-templates repository on GitHub.

If you choose to create your own Lambda function, you must configure permissions using the AWS Command Line Interface (AWS CLI). In the following example command, replace MY_FUNCTION_NAME with the name of your Lambda function, and replace REGION with your Amazon WorkMail AWS Region. Available Amazon WorkMail Regions include us-east-1, us-west-2, and eu-west-1.

aws --region REGION lambda add-permission --function-name MY_FUNCTION_NAME --statement-id AllowWorkMail --action "lambda:InvokeFunction" --principal workmail.REGION.amazonaws.com

For more information about using the AWS CLI, see the AWS Command Line Interface User Guide.

Configuring synchronous Run Lambda rules

To configure a synchronous Run Lambda rule, create an email flow rule with the Run Lambda action and select the Run synchronously check box. For more information about creating mail flow rules, see Creating an email flow rule.

To finish creating the synchronous rule, add the Lambda Amazon Resource Name (ARN) and configure the following options.

Fallback action

The action Amazon WorkMail applies if the Lambda function fails to run. This action also applies to any recipients that are omitted from the Lambda response if the allRecipients flag is not set. The Fallback action cannot be another Lambda action.

Rule timeout (in minutes)

The time period during which the Lambda function is retried if Amazon WorkMail fails to invoke it. The Fallback action is applied at the end of this time period.

Note

Synchronous Run Lambda rules support the * destination condition only.

Lambda event data

The Lambda function is triggered using the following event data. The presentation of the data varies depending on which programming language is used for the Lambda function.

{ "summaryVersion": "2018-10-10", "envelope": { "mailFrom" : { "address" : "from@example.com" }, "recipients" : [ { "address" : "recipient1@example.com" }, { "address" : "recipient2@example.com" } ] }, "sender" : { "address" : "sender@example.com" }, "subject" : "Hello From Amazon WorkMail!", "messageId": "00000000-0000-0000-0000-000000000000", "invocationId": "00000000000000000000000000000000", "flowDirection": "INBOUND", "truncated": false }

The event JSON includes the following data.

summaryVersion

The version number for LambdaEventData. Only updates when a backwards incompatible change is made in LambdaEventData.

envelope

The envelope of the email message, which includes the following fields.

mailFrom

The From address, which is usually the email address of the user who sent the email message. If the user sent the email message as another user or on behalf of another user, the mailFrom field returns the email address of the user on whose behalf the email message was sent, not the email address of the actual sender.

recipients

A list of recipient email addresses. There is no distinction between To, CC, or BCC.

Note

For inbound email flow rules, this list includes recipients for each domain that is part of the Amazon WorkMail organization in which the rule is created. The Lambda function is invoked separately for each SMTP conversation from the sender, and the recipients field lists the recipients from that SMTP conversation. Recipients with external domains are not included.

sender

The email address of the user who sent the email message on behalf of another user. This field is set only when an email message is sent on behalf of another user.

subject

The email subject line. Truncated when it exceeds the 256 character limit.

messageId

A unique ID used to access the full content of the email message when using the Amazon WorkMail Message Flow SDK.

invocationID

The ID for a unique Lambda invocation. This ID remains the same when a Lambda function is called more than once for the same LambdaEventData. Use to detect retries and avoid duplication.

flowDirection

Indicates the direction of the email flow, either INBOUND or OUTBOUND.

truncated

Applies to the payload size, not the subject line length. When true, the payload size exceeds the 128 KB limit, so the list of recipients is truncated in order to meet the limit.

Synchronous Run Lambda response schema

When an email flow rule with a synchronous Run Lambda action matches an inbound or outbound email message, Amazon WorkMail calls the configured Lambda function and waits for the response before taking action on the email message. The Lambda function returns a response according to a pre-defined schema that lists the actions, action types, applicable parameters, and recipients that the action applies to.

The following schema is an example of a synchronous Run Lambda response. Responses vary based on the programming language used for the Lambda function.

{ 'actions': [ { 'action' : { 'type': 'string', 'parameters': { various } }, 'recipients': list of strings, 'allRecipients': boolean } ] }

The response JSON includes the following data.

action

The action to take for the recipients.

type

The action type. Action types are not returned for asynchronous Run Lambda actions.

Inbound rule action types include BOUNCE, DROP, DEFAULT, BYPASS_SPAM_CHECK, and MOVE_TO_JUNK. For more information, see Inbound email rule actions.

Outbound rule action types include BOUNCE, DROP, and DEFAULT. For more information, see Outbound email rule actions.

parameters

Additional action parameters. Supported for the BOUNCE action type as a JSON object with the key bounceMessage and value string. This bounce message is used to create the bounce email message.

recipients

List of email addresses on which the action should be taken. You can add new recipients to the response even if they were not included in the original recipients list. This field is not required if allRecipients is true for an action.

Note

When a Lambda action is called for inbound email, you can only add new recipients that are from your organization. The new recipients are added to the response as BCC.

allRecipients

When true, applies the action to all the recipients that are not subject to another specific action in the Lambda response.

Synchronous Run Lambda action limits

The following limits apply when Amazon WorkMail invokes Lambda functions for synchronous Run Lambda actions:

  • Lambda functions must respond within 15 seconds, or be treated as failed invocations.

    Note

    The system retries the invocation for the Rule timeout interval that you specify.

  • Lambda function responses up to 256 KB are allowed.

  • Up to 10 unique actions are allowed in the response. Actions greater than 10 are subject to the configured Fallback action.

  • Up to 500 recipients are allowed for outbound Lambda functions.

  • The maximum value for Rule timeout is 240 minutes. If the minimum value of 0 is configured, there are no retries before Amazon WorkMail applies the fallback action.

Synchronous Run Lambda action failures

If Amazon WorkMail is unable to invoke your Lambda function due to an error, invalid response, or Lambda timeout, Amazon WorkMail retries the invocation with exponential backoff until the Rule timeout period completes. Then, the Fallback action is applied to all recipients of the email message. For more information, see Configuring synchronous Run Lambda rules.

Example synchronous Run Lambda responses

The following examples demonstrate the structure of common synchronous Run Lambda responses.

Example : Remove specified recipients from an email message

The following example demonstrates the structure of a synchronous Run Lambda response for removing recipients from an email message.

{ 'actions': [{ 'action' : {'type': 'DEFAULT'}, 'allRecipients': True }, { 'action' : {'type': 'DROP'}, 'recipients' : ['drop-recipient@example.com'] }] }

Example : Bounce with a custom email message

The following example demonstrates the structure of a synchronous Run Lambda response for bouncing with a custom email message.

{ 'actions' : [{ 'action' : { 'type' : 'BOUNCE', 'parameters' : { 'bounceMessage' : 'Email in breach of company policy.' } }, 'allRecipients': True }] }

Example : Add recipients to an email message

The following example demonstrates the structure of a synchronous Run Lambda response for adding recipients to the email message. This does not update the To or CC fields of the email message.

{ 'actions': [{ 'action' : { 'type' : 'DEFAULT' }, 'recipients' : [ 'new-recipient@example.com' ] }, { 'action' : { 'type' : 'DEFAULT' }, 'allRecipients' : True }] }

For more code examples to use when creating Lambda functions for Run Lambda actions, see Amazon WorkMail Lambda templates.

More information about using Lambda with Amazon WorkMail

You can also access the full content of the email message that triggers the Lambda function. For more information, see Retrieving message content with AWS Lambda.