How to handle incoming emails?

Question

Ruby on Rails

Tell me how to implement the following - I have a multitenancy RoR application, that is, for each "tenant" there is "its own copy of the site."
If you roughly describe part of the functionality - the application has the ability to interact by email. That is, for example, a user registers on the tenant's website - the tenant receives an email notification (address A).
The tenant can send a message to the user through the application (this message is recorded in the application and sent to the user's email from address B). The user replies to this message (through their email client) and the message goes to the return address (address B).
Address B is "listened" by mailman, processed and stored in the application (and goes to address A from address B). That is, each tenant has two email addresses - A and B. The
application must have access to address B in order to read new messages (via mailman).
Now the crux of the matter - I wanted to create an email account B when registering a tenant account, to which I could get access to read incoming messages. How can this be implemented?