Sylpheed

Georg Schmalhofer wrote:

I observed the following behaviour:

- Double-click mail in "Sent" folder > resends mail
Double-click in any other folder -> opens mail to read in a separate window

This way it is not possible to read a sent mail in a separate window. Is this intended?

Yes, it is intended. Double-click mail in "Sent" folder will 're-edit' it (as well as Queue folder).
You can still view the message in a separate window by 'View - Open in new window'.