Depending on the amount of emails and the budget you have there might be other considerations, but overall I'd recommend SQS for this. It's a well established, extremely reliable, FIFO-if-needed queueing system that scales well with any use-case. Combined with the new Lambda trigger it's a very powerful general-purpose solution.

If you would want to capture any change in your database in general and make this available to other use-cases within your company as well, Kafka or Kinesis might be a better option. Both are extremely scalable and very commonly used, Kafka might be better suited for per-event distribution to multiple topics and Java based stacks (as Python SDKs are still harder to use), while Kinesis might be the better option if you are looking for a single stream of data (vs. multiple topics with Kafka) and want to optimize for bandwidth (metric data for example).