I encountered this exact issue several years ago but was unable to solve it.

One of our staff was using an iPhone to connect via IMAP to Mercury and the lck file was not being removed even when the IMAP connection was closed by exiting the mail program on the phone.

I posted on Apple's forums about this but never received a reply. It's really poor that they continue to exercise so little control over their mail program :(

iPhone users connecting via IMAP are unable to use Pegasus Mail when in the office because their iPhones maintain an IMAP connection.  We can't figure out how to break that connection.  I was surprise that turning off the phone left the connection in an open state.  Can anyone offer advise on how to deal with this?  My web searching has not turned up anything useful.

TIA

[quote user="Brian Fluet"]

iPhone users connecting via IMAP are unable to use Pegasus Mail when in the office because their iPhones maintain an IMAP connection.  We can't figure out how to break that connection.  I was surprise that turning off the phone left the connection in an open state.  Can anyone offer advise on how to deal with this?  My web searching has not turned up anything useful.[/quote]

How is PMail configured - can your users connect via IMAP?

(As you can read elsewhere, mobiles not disconnecting seems to be a continuing problem [:(] )

PMail mailboxes are on a server and are fed by Mercury so the office PMail clients do not access via IMAP. 

The mobiles not disconnecting is definitely the problem.  I have found instructions on the web for temporarily turning off an email account on an iPhone but when working with a user he said he had done so but I still saw a connection in MercuryI and the mailboxm.lck file remained in place.  I need to get one of these phones into my hands to see I can figure anything out.