Thanks to everyone who responded to my query.
I recognise and accept that running multiple instances of PM might now be the norm but it seems a bit of overkill to me, consuming system resources (however minimal) and cluttering up the desktop with additional shortcuts and presumably the system tray with multiple icons so I'm not minded to go down that route - I'm perfectly content to run a single instance of PM, thereby monitoring only a single mailbox, and changing user as and when I need to check another mailbox.
I've adopted the suggestion about implementing a custom button in the toolbar and have put the following into a toolbar.pm file that resides in C:\Program files\Pmail so is invoked for all seven of my usernames:
0,10249,0,1806,"Change user"
0,801,0,1801,"Compose a new mail message"
0,802,0,1802,"Open or re-scan your new mail folder"
0,803,0,1803,"Work with your mail folders"
0,804,0,1804,"Open or manage address books"
0,805,0,1805,"Edit or manage distribution (mailing) lists"
0,807,0,1807,"Create or manage rules for filtering your new mail"
0,808,0,1808,"Open or browse noticeboards"
1
2,840,0
1
0,823,0,1823,"Print the current window"
0,824,0,1824,"Select a font for the current window"
0,828,0,1828,"Send all queued mail"
0,827,0,1827,"Check your POP3 host for new mail"
1
0,829,0,1829,"Both check and send mail in one operation"
Putting the 'Change user' button as the first one in the toolbar means that it's in a very similar position on the screen to the 'File' menu option, so my mouse-hand doesn't need to point the cursor somewhere completely different on the screen... [:)] It's surprising how one gets familiar with the position of certain functions on a screen, especially after using an app such as PM for the best part of 20yrs!
I've installed the new custom toolbar on both my original WinXP machine that's still running PM V4.21c and on the new Win7 machine that's running v4.70 and it seems to behave just fine in both cases, so many thanks to SvenH who originally suggested using a custom button.
Re: the issues previously caused by having the 'Change user' function in the File menu list, I assume that because the custom button is invoking the same system call (10249) there's a possibility that the issues might also occur when using the custom button, or will they.....??
Regards
--
Martin