[Users] claws-mail impap-error Port 993 tls on Macos

[David Fletcher]

At last - a solution to the Mac network issue. It appears to be a problem
with the OS logging something, which then fails, particularly in a
multi-threaded environment. That still sound vague, but the problem can
be made to go away by setting this environment variable before starting
claws:

export OS_ACTIVITY_MODE=disable

Claws then gets immediate network access without issues. Others have also
spotted this issue, e.g. here:
https://developer.apple.com/forums/thread/739571 and more on the
underlying issues here:
https://bugzilla.mozilla.org/show_bug.cgi?id=1589809

I'll sort out the patch to enable compile on MacOS after I clean up the
code in the next few days. Then we should have Claws working completely
on recent Macs.

Best wishes, David.