Email forwarding not working. (Using SES, Lambda, Route 53, S3)

Hi all,

I've tried following on from a few different tutorials online regarding a task I want to complete, which is having any emails sent to my custom domain forward to a third-party email address. Example tutorials include:

https://scripteverything.com/amazon-ses-receive-email/ https://www.daniloaz.com/en/use-gmail-with-your-own-domain-for-free-thanks-to-amazon-ses-lambda/ https://infra.engineer/aws/11-using-gmail-with-your-domain-utilising-amazon-ses-lambda

I have the created a custom domain in route 53, and the same domain is registered as a verified identify in SES. I'm trying to register an address at that domain. So, for example I have 'customdomain.com' verified, but when trying to register 'name@customdomain.com', I can not receive the messages.

I've created the rule sets, have an S3 bucket that is written to from a Lambda function (similar to the ones mentioned in the articles) and inside said function have my third-party address end points defined in forwardMapping. When I send emails to the custom domain, the S3 buckets get written to, and I get the SNS notification (which is sent directly to the third party email address) but I do not get the actual email sent to the third party address. Which means effectively I am unable to register it as a verified identity in SES since I can not receive the email. What possible steps am I missing here?