I wouldn't recommend for your own mental stability to look at /r/sysadmin when it comes to any sort of DNS or E-Mail issues. It really shows just how many bad systems administrators there are out there, who do not have a basic understanding of the systems they're using.

Just a few years ago, Atlassian required you to add an unnecessary include: record to your SPF record, and wouldn't use your domain for emails until they scanned your SPF record for that include. https://jira.atlassian.com/browse/AX-1477

You'd think companies generating as much email as Atlassian would know what they're doing.