This is how PBEM helper works:
1) If the .PBM format is used, then the e-mail subject is always "PBEM file", and there is only one attachment called PBEM.PBM.
2) If the .ZIP format is used, then the subject is "SE4 file" and there is one attachment called SE4.ZIP.
3) If the file is sent as it is, then the subject is "SE4 file" and the attachment name is something.PLR.
In the first case, when the attachment is opened in PBEM, then it will automatically decompress it into the correct SAVEGAME directory. So the Outlook rule should just open the attachment in PBEM. There should be an option in PBEM to quit after the file has been decompressed into correct directory.
In the other cases, the Outlook rules should be used to decompress or copy the attachment into correct directory.
After that the PBEM could then be executed at regular intervals to generate the turn and send the e-mails. Yes, it could be done... the hosting and sending of ready games could be done at one hour intervals, for example, and the forced turn generation once a day, even if some client file is still missing.
The only tools that would be needed are Outlook, task scheduler and PBEM, with some added features.
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PBEM