I am not sure I understand the problem correctly. If you enter just a single address, without commas, do you receive emails? If you don't, please let me know how exactly you have scheduled your backup: if by CRON, which cron script you're using, otherwise which method you're using (front-end backup, WebCron.org, custom PHP script, Akeeba Remote CLI, a third party service and which one, ...).
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!