My WordPress sites are on shared hosting, and as such, there are limitations that come with a shared hosting account, especially when it comes to sending email. In my case, my shared host keeps tighter control over the mail() function, and so limits PHP apps to sending mail via authenticated SMTP. WP Mail Bank was simple to configure and worked right out of the box. The only trouble I ran into was when I used the incorrect email credentials. I’m using the free version since my sites are non-commercial, “non-mission critical” personal sites so I don’t need the Premium features. Note that logging in the free version is very basic and this may annoy some people. But WP Mail Bank has worked very reliably since installation so I don’t really miss the more extensive logging. WP Mail Bank added authenticated SMTP functionality to my sites with no hassle, and it just works.