[ungrateful-dead]

In cost? Running postfix.org mail sever on a VM must have a nonzero cost, with the additional need to maintain the underlying OS.

[caymanjim]

EC2 micro instances are free.

[beagle3]

but are often blacklisted as SMTP sources, unfortunately.

[joana035]

Not really, only if it the IP was used to delivery spam.

But IP reputation can be established with a bit of warm up and human interaction.