Just throwing my 2c in the ring: I've been using iRedMail for I want to say 10+ years now. Just simple linux no-frills webmail with nice admin and default webmail. Best part is it is dead simple to set up, the developer is very nice and responsive on his forum and it has been rock-solid. Granted, I don't send a lot of mail from it but it has been running as a journal for many years without issue. I do send some mail from it--mostly from devices--to my gmail and have never had a problem with blacklisting. I think this mostly depends on your IP reputation so your host and how you host it is important.