The emails aren't from iTunes. They're sent out randomly by fraudsters who know that at least some of the addresses they use will be valid and that at least some of the people at the valid addresses will use iTunes.
There are two possible purposes:
(a) to get people to pay money for fake invoices ; or
(b) to get people to open attachments (such as receipts in pdf format) which immediately dump MALWARE onto their computers.
If you've opened any attachment received with such an email, you should immediately carry out a full scan with your anti-virus software and a further one with Malwarebytes:
https://www.malwarebytes.com/antimalware/