How to implement multi tenancy with Amazon SES

In this blog post, you will learn how to design multi-tenancy with Amazon SES, as well as the fundamental best practices for implementing a multi-tenant architecture that can effectively handle bulk the email sending needs of your downstream customers.

Amazon Simple Email Service (SES) is utilized by customers across various industries to send emails to their recipients. Often, they need to send emails on behalf of their downstream customers or for other business divisions. Organizations commonly refer to these use cases as “multi-tenant email sending practices. To implement email sending multi-tenancy practices (i.e. to send bulk emails on behalf of end customers), Amazon SES customers need to adopt an architecture that enables them to effectively meet the email sending needs of thousands of downstream customers while also ensuring that the email sending reputation of each customer or the tenant is isolated.

Use cases

Onboard multiple brands from different Business units (BUs) with different domains.
Separate marketing and transaction tenants.
ISV Customer’s requirement to segregate email sending reputation of their end customers.
Domain management via configuration sets.
Track individual customer’s email sending repurataion and control their email sending process.

Prerequisites

For this post, you should be familiar with the following:

Solution Overview

In the email ecosystem, domain and IP reputation are critical in getting emails delivered to the inbox. Tenants in a multi-tenant scenario might be unique businesses or an internal team (eg marketing team, customer service team and so on). Because the maturity of each tenant varies greatly, implementing a multi-tenant environment may be increasingly complicated and difficult. While one tenant may have a well-validated and highly-engaged recipient list, another tenant may have an untrusted email recipient list, and sending emails to such email addresses may result in bounces or spam, lowering the IP and domain reputation. So, organizations have to build safe guards to prevent an unsophisticated sender or a bad actor from impacting the other tenants.

To better understand multi-tenancy, let us first look at how Amazon SES sends emails. Any emails sent via Amazon SES to end users are sent using IP addresses that have been mapped within Amazon SES. Amazon SES offers two types of IP addresses: shared IP addresses and dedicated IP addresses. (Currently Amazon SES offers two kinds of dedicated IPs, which are 1/ Standard dedicated IPs, 2/ Managed dedicated IPs). Shared IPs are shared across many SES customers, and all your emails are sent using shared IP addresses by default unless you have requested for dedicated IPs. Dedicated IP addresses/addresses are designated for a single customer or tenant, where the tenant might be a business unit within the customer’s own eco system or a downstream customer of an ISV.

If a customer is using shared IPs to send email via SES and trying to achieve multi tenancy, then they can do so to segregate the business functions of multiple tenants such as tenant tagging, SES event destination routing, cost allocation for each tenant, and so on; but it won’t help to manage or isolate email sending reputation from one tenant to another. This is because; these shared IPs are mapped to an AWS region and incase one rogue tenant is trying to send spam emails then it will impact other customers in the same region who are using same set of shared IPs.

If you are an Amazon SES user and wish to separate the reputation of one end-customer from another then dedicated IPs are the ideal solution. Dedicated IP or Dedicated IPs (also known as dedicated IP pool) can be assigned to a tenant, and the email sending reputation for that tenant can be readily isolated from that of another tenant. If tenant one is a problematic sender and internet service providers (ISPs) such as Gmail, Hotmail, Yahoo and, so on, flags the respective domain or IPs, the reputation of the other tenants’ domains and IPs are unaffected since they are mutually exclusive.

Amazon SES supports multi-tenancy primarily through two constructs: 1/configuration sets, 2/Dedicate IP pools. Configuration sets are setup rules that are applicable to your verified identities, whereas dedicated IP pool is to group dedicated IPs into a pool, which can then be mapped to a configuration set, such that the respective Identity/Identities may only utilize the same IP Pool without affecting other tenants. Let’s now witness a simplified architecture view.

Multi tenancy using a single AWS account

In this architecture, if you notice tenant 1, tenant 2 and tenant 3 are using the distinct configurations with respective dedicated IPs while tenant 4 is using shared IPs. i.e. the tenants can chose which configuration sets needs to be used for their domain. This provides customers capability to achieve multi tenancy.

Amazon SES multi tenancy – best practices

Always proactively reach out to your account team or raise a support case under “service limit increase” category informing that you will be sending on behalf of tens of thousands of customers. This will help AWS in rightly setup limits within your account and be cognizant of your sending patterns.

While the architecture described above will most of the time help Amazon SES users manage multiple end customers effectively, in rare cases; Amazon SES users may receive a notification from AWS support stating that their Amazon SES account is being reviewed. This indicates that your Amazon SES account is being used to send problematic email to end recipients, or that the account has been paused (if you haven’t reacted proactively upon controlling the faulty senders within the review timeframe), which means you can’t send email from your SES account because your spam or complaint rate has exceeded a certain threshold. These type of situations occurs because, Amazon SES sanitization process is implemented at the AWS account level by default. So, even if any of the tenants using a dedicated IP or a dedicated IP pool and their spam or complaint rates exceed the approved SES limit, Amazon SES sends a notification to the account admin, flagging the concern in their account. In such cases, it is recommended to implement a process known as “automatically pausing email sending for a configuration set“. You can configure Amazon SES to export reputation metrics that are specific to emails that are sent using a specific configuration set to Amazon CloudWatch. You can then use these metrics to create CloudWatch alarms that are specific to those configuration sets. When these alarms exceed certain thresholds, you can automatically pause the sending of emails that use the specified configuration sets, without impacting the overall email sending capabilities of your Amazon SES account.

If you are an Enterprise ISV customer and you have tens of thousands of downstream customers then there is a possibility that you will hit Amazon SES provided maximum quota. In those scenarios you have two options; 1/ Ask for an exception for your AWS SES account – In this approach, you need to request AWS to increase your quota applicable for the existing account to a higher threshold and depending upon your previous usage and reputation AWS shall increase your account limit to accommodate more customers/tenants. To do this you need to raise an AWS support case under “service limit increase” and present your requirement on why you want to increase your Amazon SES account quota to a higher limit. There is no guaranty that the exception will always be granted. If your exception request is denied, you must proceed to the second option, which is to 2/ segment your customers across multiple AWS accounts. In this approach, you must calculate your customer base ahead of time and distribute your downstream customers across multiple accounts within the same AWS region in order to set up their email sending mechanism using SES. To better understand option 2, refer to the architecture diagram below.

Multi tenancy using multiple AWS account

In the above architecture various tenants are connecting to Amazon SES in different AWS accounts to implement multi tenancy. Email event responses can be taken back to a central data lake located in the same AWS region or in different region. Furthermore, as shown in the diagram above, all AWS accounts mapped to different tenants are under a Parent AWS account; this hierarchical structure is known as AWS Organizations. it is recommended to use AWS Organizations which enables you to consolidate multiple AWS accounts into an organization that you create and centrally manage. It helps in security and compliance guide lines, managing consolidated billing for all the child accounts.

Conclusion

Appropriate multi-tenancy implementation within Amazon SES not only helps you manage end-customer reputation but also aids in tracking usage of each user independently from one another. In this post, we have showcased how Amazon SES users can utilize Amazon SES to manage large number of end customer, what are the design best practices to implement multi-tenant architecture with Amazon SES.

Satyasovan Tripathy works at Amazon Web Services as a Senior Specialist Solution Architect. He is based in Bengaluru, India, and specialises on the AWS customer developer service product portfolio. He likes reading and travelling outside of work.

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