Email copies of forum postings do get delivered but take ages to load in the email client, well about 10-20 seconds, which is an age in email terms, meanwhile freezing the client (Outlook or whatever). Presumably it's something in the html of the email message, but other html emails arrive and appear just fine.
I know it sounds like that's not a Moodle issue, but rather something with the email client, but hear me out: it happens with emails from forum postings but not other emails sent by Moodle cron (e.g the 'Welcome to the course...' emails), it happens in this same way using different email clients (Outlook, web mail etc), and it happens with emails sent from totally different moodle sites (including from moodle.org).
It's very frustrating, such that users end up ignoring emails or unsubscribing.... Help. ideas...?