Thanks. Seems SSL/TLS is involved. Turned it off and this worked for most accounts. For the last I renewed the passwords and this seems to have solved the last.

Also repaired the 4.80 install, knowing now that I couldn't brake anything.

If I've another moment I'll reimplement SSL/TLS.

Thanks for the guidance. 

I had a BSOD caused by a different program. After the reboot most of Mercury works. However the IMAP server doesn't accept any connection. The window is visible, but no attempt of any device connecting is visible.

Further

- last mercuryI Session and Log dates from before the BSOD

- disable and enable mercuryI protocol didn't help (+restarts of merc)

- no lock files in user mailboxes

- changing a protocol setting , OK, set it back, OK didn't help

- IMAP devices (android) didn't show a message

- PMAIL to imap: the IMAP server that manages this mailbox or folder has reported an error during operation you attempted to perform. The operation cannot be completed.

 I do have some dmp files, which I'm about to send to the emailaddress I noticed somewhere in the forum.

Maybe someone has an idea on what to change as I have no idea left on what to do. And I'm not to sure on what happens when doing a reinstall.. I've strong hope the solution may be simple...

First make sure that MercuryI is set to listen on the correct port (143). Switch off SSL/TLS support to eliminate that as an error source. Make sure "IP interface to listen on" is blank.

If you still can't connect after restarting Mercury then stop the program, make a complete backup of the Mercury folder, and run the installer, selecting to update. This will replace all executable files in case any of them were damaged in the crash. All your settings should be untouched. If you aren't already running version 4.80 I would suggest that you upgrade to it.