Here is a script to avoid this issue. You may want to replace the /usr/bin/sylpheed with this script and rename the original binary to sylpheed.real so that there's no need to change the sylpheed.desktop.
Here is a script to avoid this issue. You may want to replace the /usr/bin/sylpheed with this script and rename the original binary to sylpheed.real so that there's no need to change the sylpheed.desktop.