I use the provided backup script to run a backup on a regular basis, and made some changes to it so it will stop the hmailserver service first (including checks to find out whether it is actually running etc.).

But I'm actually wondering about one thing: what happens when hmailserver is in the process of fetching mail from an external account, and the service is stopped? If a mail is being downloaded from the external server at the same time, will hmailservice finish that task fist, or will it cancel and resume at the next fetch? Or is there a chance that the mail will be half-fetched and corrupted? (that's my point of worrying...)

And is there any difference between stopping the whole hmailserver service and just stopping the server itself via scripting? Currently I'm using the script to stop the whole hmailserver service before starting the backup, and I noticed that it is also possible to stop the server without stopping the complete hmailserver service. Will it make any difference to the backup process? What is advisable?

Hopefully someone can help me out, thanks!

Email servers are resilient, if the email is only half downloaded, the sending server will resend it again. The sending server requires an OK from the recipient server to say that it got the whole email. If it doesn't get that then the sending server should re-queue it and try again later.