CleanTempMail uses Go and MongoDB, but the choice of language and database is only part of running an email receiver. The important design questions concern when a message is considered accepted, how it is retrieved and what happens when storage is busy.
Define acceptance and durability
A receiver should have a documented policy for persisting accepted mail and handling temporary failures. Unacknowledged database writes are not a shortcut to reliable delivery: they make it harder to know whether a write succeeded. Choose durability settings according to the service's recovery requirements and validate them under failure conditions.
Index the actual read paths
Inspect the queries used for inbox listing, message lookup and cleanup. Select indexes that support those queries and measure their read and write cost. Avoid creating an index merely because another service uses it.
Use expiry with realistic expectations
MongoDB TTL indexes can remove expired documents in the background. Deletion is not immediate and consumes resources. Expiry of a stored message does not disable its recipient address or remove copies in unrelated logs, exports or backups. See MongoDB's TTL documentation for behavior and limitations.
Bound concurrency and queues
Limit incoming connections, parsing work, recipient amplification and concurrent storage operations. Reuse database clients and size connection pools using measurements rather than a universal pool-size recommendation. A retry queue needs a bounded worker count and observability for age as well as length.
Separate inbox updates from delivery guarantees
Server-sent events can update a connected browser after a message is processed. They do not remove sender queues or network latency. Programmatic clients should follow the current API documentation, including access and request limits.
Compare designs using representative traffic and failure tests. This article does not supply a benchmark establishing that Go or MongoDB is universally faster than an alternative stack.