Hi,

If you want to raise Warning just for information and then allow to save record, 

do not use @api.contrains and donot raise Warning that will not allow you to save record.

Instead 

You have to do that on onchange method like this way 

https://github.com/odoo/odoo/blob/4909e87cd463c3bedcf096e0535ec90d829aa491/addons/sale/models/sale.py#L373

Before buy i need to know the new question.

Odoo work with catchall and bouncer system mail.
Then, i see odoo send with names like bounce+1a8234932@domain.com and etc
This module, where save mails? what folder? if odoo not use static account?