Hosting your own mail server and sending any kind of automated mail is a whole new can of worms. I used to run a RSS-to-email for my blog using Mailchimp's free service. It was limited to at most once-per-week mail with a summary of any new blog posts and not pushed onto readers by any kind of obtrusive pop-ups or annoying stuff like that. Mail was sent through Mailchimp's servers, but signed with my own personal domain's DKIM key. I started getting delivery problems when sending personal (non-automated) mail from my domain to gmail addresses. One of the few reasons I could think of was people "unsubscribing" from my RSS-to-email by marking it as "spam" instead of clicking the unsubscribe link. I'm guessing that with the low volume of mail I'm handling even a single person doing that might put the domain on some naughty list. I don't have solid any proof that was the cause. Gmail never tells you what's wrong. However the delivery problems went away some time after I shut the RSS-to-email thing down. Maybe a coincidence (I also did some changes to my DMARC config at approximately the same time to try to address the issue), but I'm now very afraid of sending out any automated mail associated with my domain.