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Lots of BYE Courier-IMAP server shut down by signal. errors

mhi1
Dabbler
Posts: 14
Thanks: 1
Registered: ‎24-02-2021

Lots of BYE Courier-IMAP server shut down by signal. errors

I use (on different computers and tablets and phones) several different email clients (apps) to access my incoming PlusNet email, all using IMAP. They all suffer delays and disconnections, some coping with unexpected disconnections better than others. All the ones where I can see a trace of the IMAP network traffic keep ending with the same response, * BYE Courier-IMAP server shut down by signal. What does it mean? How can I (or PlusNet) get my email to operate without long pauses to recover?

From the email client with the easiest-to-see tracing, here is a not untypical fragment from its log data which is then followed by the network connection to the server being lost.

[16:59:02] IMAP4> 426 UID STORE 49440 +FLAGS.SILENT (\Seen)
[16:59:02] IMAP4< 426 OK STORE completed.
[16:59:08] IMAP4> 427 UID FETCH 49441 BODY.PEEK[]
[16:59:08] IMAP4< * BYE Courier-IMAP server shut down by signal.

I have fed the text into a world-famous search engine, and it finds the BYE message (only) in what looks like an old version of the Courier mail server. I don't think the problem is with any timeout parameters I can set: as you can see in the trace, it's just 6 seconds between the 426 OK response and the un-numbered * BYE response.

In case it helps: imap.plus.net, SSL enabled and using STARTTLS command, port 993, with an appropriate PlusNet mailbox name and password.

Is PlusNet perhaps using an out-of-date version of the IMAP mail server?

 - Mark