This is a fun hack, but there is no way I would get involved in providing any form of commercial email service for $1440 arr. I wouldn't do it for $1440 a _day_. Everything involved with email is pain. I wish you luck.
Agree. Even if you comply with most important technical standards/requirements you still need to spend a lot of time overseeing your system, and researching best practices and recommendations that directly affect domain and IP reputation, to avoid getting blacklisted.
Shameless plug: A while ago I decided to try build a home made SMPT Mail submission component for better understating what's going on under the hoods (and for "fun"), it was really though, and once I was able to send a DKIM verifyed e-mail to GMAIL servers I called it a day and moved on [1]
[1] https://thomasvilhena.com/2020/01/mail-submission-under-the-...