Incoming Email configuration

I am having a bit of a difficulty understanding how “incoming mail” configuration is defined.

The way I understood by looking into the source, sentry run smtp starts a daemon which binds to port 1025 (by default), and this daemon speaks smtp natively on port 1025. It parses all emails that are sent to it, and identifies the emails from which Sentry needs to parse content.

Does my understanding look correct?

Isn’t be surprised if this still works. I wrote it many years ago, and we never used it ourselves in production. But yeah, your understanding is correct.

I managed internal smtp working. But was surprised, that I was not able to reply back on notification e-mail as is, as the length of the reply must be no more than 2000 character.
The value is hardcoded and unmanageable.

What is the other option apart from Mailgun?