Reoccurring BAD internal server error

Hi,

We’re experiencing an intermittent issue with the IMAP connection in the Postie plugin. Randomly, Postie starts returning:

fetch_mail: Connecting to :993 (imap-ssl)
pConnection: mailbox: INBOX
Connecting via Socket
Socket: tls://:993
Socket error: 0 - (Resource id #23)
Socket: IMAP
socket write: A0001 CAPABILITY
checkOS: Linux
socket read (3) :* OK IMAP4rev1 proxy server ready
socket write: (login) LOGIN/APOP/PASS
checkOS: Linux
socket read (1) :* BAD internal server error
fetch_mail: IMAP - Could not connect to IMAP server on port 993. Array
(
[0] => * BAD internal server error
)
doing postie_session_end
memory at end of email processing: 4529720

The only workaround we’ve found is to switch the connection method from Sockets to cURL, save the settings, then switch it back to Sockets again. After doing this, IMAP starts working normally until the issue reoccurs later.

This behaviour appears random and there are no obvious mail server issues at the time it happens.

Have you seen this before, or is there any known cause/fix for it?

Thanks