My Forward Email is being Tracked ?

Hello everyone,

I recently received an email containing some attachments word and pdf (say from A) to my personal email address (say
B) that i forward to my another Email Account (say C).

Later i found that the first email sender (A) got to know somehow that who i(B) am forwarding this email to.

It seems that A is tracking my email forwading that i am receiving from him. Is there a way to do so ? if yes please let me know and how i may protect it in future.

I am a computer illiterate. I hope that i have been able to explain my problem well.

All your help is really appreciated!
Thanks in advane