On Thursday, 05 January 2023, we received notification that one of the email servers used by JiscMail was listed on a global spam "blacklist", causing recipient mail servers to start rejecting JiscMail posts.

We reported the issue to the operators of that email server, and worked with them to ensure that the server was removed from the list. By 09:00hrs on Friday (06 January) it was confirmed that the server had been removed from the blacklist, and that normal service had resumed.

Unfortunately, later that day, the server was re-added to the blacklist, causing recipient servers to start rejecting messages once more.

Due to the way in which the software underpinning the JiscMail service works, after several bounced or rejected messages to an individual email address, the software assumes that the address no longer exists and removes it from any subscribed groups. This had the effect of removing around 50,000 subscriptions to just short of 500 JiscMail lists.

We are pleased to inform you that, as of 14:00hrs on Wednesday, 11 January 2023, we believe the root cause of the issue (the blacklisting) to have been resolved, and are in the process of resubscribing all affected users. We expect this to be completed by no later than 17:00hrs on Wednesday, 11 January 2023.

Despite these issues having been addressed, subscribers and list owners may continue to recieve error messages that have been "queued" by mail servers outside of our direct control. These are expected to have fully cleared by Friday, 13 January 2023.

We apologise for any inconvenience caused during this time.

Update (13:15 12/01/2023): We have identified a secondary issue, causing the client servers to retry sending posts repeatedly, this results in subscribers receiving "duplicated message" errors on every retry.

We are continuing to investigate the issue and are working on reducing the impact to list owners and subscribers as far as possible.

We, again, apologise for any inconvenience caused, and will continue to update you on this issue via the Jisc and JiscMail Twitter accounts.

Update (09:00 13/01/2023): Further investigation has shown that communications to the mail servers that support JiscMail (and other global services not provided by Jisc) are not being "completed" as expected.

From what we've seen, the situation arises as follows:

1. A user sends an email to a list address;
2. The user’s mail server successfully "handshakes" with the JiscMail mail servers, and sends the data – but receives no acknowledgement, causing the connection to hang and eventually timeout;
   (The JiscMail mail server has successfully received the message at this point, and posts it to the list, however...)
3. The user’s mail server assumes, due to the dropped connection, that the message wasn’t delivered successfully, so retries after a defined period of time (circa 15 minutes, in most cases);
4. This process continues (loops) until the user's server either receives an acknowlegement, or reaches a pre-defined time limit, where it gives-up (a couple of days, in some cases).

In addition, every time the user’s mail server attempts to deliver the message (and times-out), the JiscMail platform automatically responds to the user with a "Duplicate post" error report, further adding to the number of messages in transit.

Unfortunately, we have no way of preventing the "Duplicate post" messages being sent, but have reported these findings to the vendors of the software that underpins JiscMail, and are working with them to resolve the situation as soon as possible.

Update (20:15 13/01/2023): The software vendors have informed us that things are returning to normal, and that they will continue to monitor things over the weekend.

We'll continue to monitor our mailboxes, and will provide updates where appropriate.

Once again, thank you for your continued understanding.

Update (08:00 18/01/2023): Please accept our apologies for the lack of update; we really have been doing everything to resolve the situation as quickly as possible.

As it stands, there are two major ongoing issues:

1. Emails to list addresses appear to send correctly, but eventually receive a "timeout" or "rejected" error report; and
2. Posts submitted to lists directly from the website claim to be successful, but don't actually "post"

The end result of both is that messages fail to be distributed to subscribers, or to the list archives (where applicable).

We're continuing to work with the software vendors to identify the root cause and apply a fix, though this is taking far longer than anticipated.

Update (08:45 19/01/2023): We're making progress...

At 16:46 yesterday, we received notification that the software vendors had been able to un-block communications from Microsoft365-based email domains, enabling email traffic to start flowing again.

There's quite a queue that's built-up over the last week-or-so, so messages may take a while to come through, but early indications are that they ARE coming through.

There's some good news on the website-based posting front too, with a number of users reporting that messages posted to lists via the JiscMail website having also been delivered successfully.

We'll keep monitoring the situation, but things are looking positive.

If, however, you've tried to post to a list AFTER 17:00 yesterday, and have subsequently received an error message, please contact help@jisc.ac.uk, quoting "Ongoing JiscMail Issues".

Update (09:30 24/01/2023): At this time, we believe the vast majority of issues experienced over the last couple of weeks have been resolved.

Anyone affected by the earlier "Unsubscribe" issue should now be re-subscribed to their chosen lists, the "Duplicate Post" messages should have stopped, and users should be able to post to their appropriate lists via email or the website without any great delay.

We would like to, once again, apologise for any inconvenience caused over this period, and thank you for your forbearance and understanding.

Should you continue to encounter difficulties, please report them to help@jisc.ac.uk in the normal manner.