If you've got a lot of domains, but need the `admin@<domain>.<tld>` registration emails to work correctly, you can route them all through SES + Lambda for nothing, rather than having to add hosting to all the domains. Impl works well for some use cases.
Would you have some more info on how to set this up ?
Then route your messages into S3, mount the bucket using s3fs, and point Dovecot at it (Maildir) to enable IMAP. Or just use a MUA that could read a Maildir directly.
Going the other way, you could configure Postfix to relay via SES.