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No, this is not a bug, it's just the consequence of your mailservermail-server closing the connection to JEMH/C whilst the mail was still being read (by JEMH). It is not caused by JEMH/C and cannot be solved by JEMH/C. See Impact and Migration steps possible:
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When a FolderClosedException occurrsoccurs, it stops all mail processing, specifically, as the mail was not read fully:
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Your mailserver can drop connections for a variety of two main reasons:
Too many concurrent logins using the same account
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Your mailserver may simply kill off the one that is oldest, which was unfortunately still in use.
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The mailserver may determine the connection ‘dead’ if it takes too long. This can be a big problem for some IMAP servers.
For (1) To check if this is a problem, count how many inbound mail servers you have defined using the same account. If its more than 15 you could be affected.For (2)
Mails are taking too long to download
The mailserver may determine the connection ‘dead’ if it takes too long. This can be caused by large emails for some IMAP servers. See IMAP batch sizes too low, below for background, steps to verify if this problem affects you, and action you can take to increase the default batching size .as described in Download performance of POP vs IMAP
Background
JEMH Auditing
Current versions of JEMH prevent the ‘download’ button operating and show the following information dialog:
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