+1 for this feature.
Ideally I might want to send out separate newsletters from separate segments and use different smtp providers for those.
usecase a: im managing mailings for different small sites/client - and I want them to be sent from physically separate smtp servers. Because some client might be paying for bluehost smtp for example and another for mxroute smtp.
usecase b: combining free tiers from different companies. send 500 from mailchip, then 1000 from sendgrid then 100 from mailgun.
as of right now. I think I just have to setup mautic instance separately for each domain. and Im seeing others have this problem as well: One Mautic installation for multiple domains?