My web application has to send emails, and it's hosted on multiple physical servers. Using a third-party service is not an option, so I'm installing postfix (or maybe sendmail).
Is it more common in this case to install postfix on a central server, or to install it on each app server? I'd imagine the latter would be easier, requiring less networking/security configuration (and I'd use chef or something to deploy it to all machines at once). Are there disadvantages to this approach?
One potential problem that crossed my mind is whether it'd make it more likely for the message to get flagged as spam, but AFAICT I could set up a reverse DNS for each server and alleviate that problem? Anything else I'm not considering?
Using a third-party service is not an option
- Why not? Is it a cost issue? If so, most email relay providers offer a free tier.