Delete mail queue in hmailserver
Hmail store mails in folder
C:\hMailServer\Data\
Delete all .EML files from Data Directory. Do not delete folders inside Data, that is users data.
Go to Data Directory (C:\hMailServer\Data\) in command prompt and run below command.
cd "C:\hMailServer\Data\" del *.eml
If you have lot of mails in queue, it may take some time to finish.
See hmailserver