Earlier quoted context omitted.
1. Yes, most people will tell you not to host your own email, because its too complicated/difficult to get your mail delivered reliably. A lot of this is FUD. Yes, email is a bit more difficult to get right than say, hosting a web app behind Nginx. It's an old protocol, with many "features" bolted on years later to combat spam. I'm not sure how email is easier to "hack," unless there is a zero day in Postfix or somet…
> DKIM records and proper signing of outgoing messages (DMARC records help too) I've read somewhere that spammers started to use DKIM (or was it DMARC?) records faster than the legitimate web-mail providers.
If the sender is passing as an authorized sender (DMARC aligned), then the receiver has a pretty good indication the email is legit and that the sender was delegated to sent email on behalf of the domain. If the email is then classified as spam (based on its contents), then it is easier for the receiver to choose whether to adjust the reputation of the domain (in case of DMARC alignment), or the IP (if not aligned).
A DKIM signature and DMARC alignment is no guarantee that the email passes spam filters. The whole point of DMARC is to give the receiver as much information as possible to make a confident decision on the legitimacy of the email, and the reputability of a domain.
DMARC and DKIM works both ways, if you are sending legit email (not spam), it will improve your deliverability, but if you are in fact spamming then DMARC will reduce your deliverability (as it should).