First all, thank you for delivering this great form plugin!
The scenario... I'm a fan of backups, and as a webmaster working with several websites using your plugin, I do lots of changes, improvements and updates to the contents, sometimes including forms, and when it comes to backup forms with your plugin, special care must have been taken, because every website backup their forms with the same, universal, file name: contact-form-backup-all.txt
Now to the request... It would be really sweet and it's actually very easy to implement by you, that the filename include the domain name, do you can rest assured that the bunch of backup files in your Download folder is perfectly sorted. The proposed filename would be:
You get the idea. I'm sure this may be very useful to others too.