I don't know about the rest, but surely the race conditions are the fault of whoever designed the concurrency part. An email client does not inherently have race conditions.
> assume it is the single client that will operate that account
You are still making wild assumption without actually thinking about what means to writing an email client.
> assume it is the single client that will operate that account
You are still making wild assumption without actually thinking about what means to writing an email client.