On Thursday evening, Spamhaus blocked our main email server for 4 hours. They did so again starting around 12:24am this morning, pacific time. When this happens, the only information I'm given is the approximate time they received a suspect message and that they had received only one message in the 24 hour period.
When this happened on Thursday night, I spent the evening trying to isolate the email address that may have triggered the listing. Given that we send upwards of 17M emails a day, this can be tricky. I came up with a set of possible email addresses. I disabled those accounts, and sent each an email message directly, asking them to verify that they wished to be on a Groups.io email group.
Clearly I did not locate the correct email address, and we were listed again. I'm going through the logs, looking for the needle, but it's challenging. I have attempted to contact Spamhaus. I hope they get back to me.
It appears most places are no longer blocking us because of this listing, although an ISP in Italy is still blocking us.
Unrelated, Charter.net has not been accepting email from our main email server since Friday. I have been trying to contact them.
I'll update when I know more.