HamRadioDeluxe is a great ham radio software suite with a lot of dedicated tools and features. Its HRD Logbook has also capabilities to sync with other databases including LOTW, eQSL but also http://hrdlog.net. I had some problems with hrdlog.net which was caused by blacklisting of one of their servers. It took me some time to debug but finally Mike VK4EIE provided the important info that data is uploaded to mail.hrdlog.net (instead of just hrdlog.net). It is not any email protocol used but just port 80 (html) for that purpose. For some reason mail.hrdlog.net was blacklisted and therefore caused upload fails. After mail.hrdlog.net was whitelisted the software worked perfect for the purpose.
Lessons learnt: In the good old days, hams were busy to fix problems with their transceivers or antennas. Today, we spend more time to fix software or Internet issues.