Failed to send emails that I never sent

Some months ago, I started to receive some emails from “Mail Delivery Subsystem” (mailer-daemon@googlemail.com). Despite this is “automatic” failure email, I thought these emails were spam, so I just ignored. But today much more emails, and this started to disturb me.

These emails are send from mailer-daemon@googlemail.com (there is a icon that indicates a reply email) and says that “MYEMAIL@aol.com couldn’t be found”. “MYEMAIL” is the email that is receiving these messages, but with domain “aol.com” (I don’t have any email from this domain).

In these emails, there is always a attached file about something attractive, like diets and wines. I think the most curious detail is that I was receiving these emails but in a “normal way”. Before receiving from mailer-daemon, I was receiving like normal spam, even with the same subject, and at some point this has changed to mailer-daemon. Another detail is despite these emails always have a attached file, I can’t see the attached file icon’s until I open the email. Only then, when I close the email, I can see the attached file icon’s. Obviously I never downloaded these files

I already changed password, checked login’s entries and everything seems to be normal. I can just block emails from mailer-daemon@googlemail.com, but I’m concerned about why this is happening.