In order to more quickly get to the bottom of this, please can I ask people who are affected to post a message here with the details requested by Igor in
http://forum.parallels.com/showthread.php?t=106113
Basically (without changing the headings - post info below each heading please) we need posts with this info:
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PRODUCT, VERSION, MICROUPDATE, OPERATING SYSTEM, ARCHITECTURE
PROBLEM DESCRIPTION
STEPS TO REPRODUCE
ACTUAL RESULT
EXPECTED RESULT
ANY ADDITIONAL INFORMATION
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Under the ANY ADDITIONAL INFORMATION heading, please can you provide as much info on the iPhone being used as possible? .e.g Type (e.g. iPhone 4s) and iOS version. But please post even if you don't have this information to hand. We need to see if there's any correlation in terms of Plesk version and OS etc etc.
ALSO please include information on the firewall you are using. e.g. Plesk firewall, APF, some other firewall.
It might be helpful also to include details of any third-party utilities or applications that you might have installed, e.g. clamav, qmail-scanner, spamdyke....anything that might have any effect whatsoever with email, even if it isn't something you'd expect to directly come into the equation with IMAP.
Please also post as much info as you can on the actual error messages (if any) that the user encounters on their phone, or any errors mentioned in any logs (if there is anything logged -- which doesn't seem to be the case).
[zconsulting -- sorry, I'm not sure about that setting]