Thanks for your post.
We had few reports from our customers that PST Creator was taking too long to process some specific messages. After troubleshooting, we have found that any message addressed to a large number of recipients (i.e. 2000+ recipients) was slowing down the conversion process. Unfortunately, the Outlook API takes unable to handle it properly.
In order to prevent this behaviour we have implemented a workaround to limit message recipients.
PST Creator has Advanced option to limit message recipients. Default value is checked and maximum recipients set to 50. You can configure it by pressing ‘Advanced’ button in ‘Settings’ page. See the Users Guide (page 12) for more information. When enabled, the complete recipient list will be added as a message attachment.
but I am curious if there is a limitation of the tool itself. For example, 100 recipients?
As said earlier, test shows 2000+ recipients slows down conversion process. You can set the value to your needs. Perhaps set a maximum (i.e. 200, etc) value, if conversion process slows down then reduce the number.
Hope this helps.