Now resolved.
There are likely to be many instances of forum emails (notifications, new user requests) failing to be delivered during the next 24-48 hours. When I am confident that the problem has been resolved I will make another announcement.
TL;DR
The IP address of my email server has been blacklisted by Spamhaus Zen. Hence many emails sent by my server are being rejected by recipient servers.
This is due to my static IP address being changed when I moved house on Tuesday, and me just discovering that the new address is not on the list of IP addresses that are permitted to send email.
Thanks a bundle Plusnet - again!!!
Plusnet will be "investigating the issue" one their customer service department re-opens Friday morning, and will report back at some point. Until I hear back, it is not worth the hassle of requesting a delist from Spamhaus, as I'll only end up back on the blacklist if Plusnet haven't got their finger out and removed me from their "non-MTA" list.
Welcome to the Cumulus Support forum.
Latest Cumulus MX release v3.2.3 build 3059 - 04 December 2019.
See the Wiki for downloading either version.
Latest Cumulus MX release v3.2.3 build 3059 - 04 December 2019.
See the Wiki for downloading either version.