What is the maximum number of rules allowed in an AWS SES rule set?

Based on the information available, there appears to be a limit of 1000 domains across all rules in AWS WorkMail inbound rules. This is indicated by an error message that states "Number of emails/domain exceeds maximum limit: maximum allowed: 1000."

For SES Mail Manager rule sets specifically, there isn't an explicit maximum number of rules mentioned in the provided sources. However, each rule can have multiple conditions, exceptions, and actions, which might help you optimize your rule structure.

If you need to handle routing for a large number of tenants, here are some recommended practices:

1. Combine rules where possible by grouping similar routing requirements together. For example, if multiple tenants need the same action, you could create a single rule with multiple domain conditions rather than separate rules for each tenant.

2. Consider using SES Mail Manager, which was specifically mentioned as "an easy to use and configure mail routing solution" with WorkMail as a delivery option.

3. Structure your rules efficiently by leveraging the ability to have multiple conditions and actions per rule, which can help reduce the total number of rules needed.

Regarding increasing the limit via a service quota request, the sources don't specifically mention whether this particular limit can be increased. Some AWS service quotas are eligible for increases while others are not, but this specific limit's eligibility isn't clearly stated in the provided information.
Sources
Workmail - DomainName - Organization Settings - Inbound Rules. Limit 498 on list of rules, error limit 1000 | AWS re:Post
Rule sets and rules - Amazon Simple Email Service

Quotas for email receiving in SES and which of them can be increased are documented in this documentation section: https://docs.aws.amazon.com/ses/latest/dg/quotas.html#quotas-email-receiving

The maximum number of rules in a rule set is 200, and you can have 40 rule sets in an account. Both quotas aren't possible to increase.

For scaling out your environment, one simple option would be to host the number of tenants in each account that it can accommodate and to create new accounts when the number of tenants exceeds that limit. This will also avoid other issues, such as the programmatic management of your SES configuration starting to exceed API call limits when the number of configuration elements grows with your tenant population.