Linux Monitoring

I hit a sacred linux computer of which I dispatched an e-mail from (account A) to added telecommunicate come statement (account B) of mine on a assorted mutual patron and I did successfully obtain the telecommunicate in statement B. However, from statement B, I also conventional a MAILER-DAEMON telecommunicate from my computer stating:

I’m afeard I wasn’t healthy to have your communication to the mass addresses.
This is a imperishable error; I’ve presented up. Sorry it didn’t impact out.

abc@abc.com:
Sorry, no box here by that name. vpopmail (#5.1.1)

I don’t undergo who abc@abc.com (email denaturized for privacy) is and I never modify e-mailed this person. Does this stingy my computer is hacked or has a telecommunicate bot predominate my accumulation computer or something?
Sorry I meant to land that I had conventional the MAILER-DAEMON telecommunicate in my Account A, with the aforementioned returned communication on the lowermost as the telecommunicate I had dispatched to Account B!

how crapper i country telecommunicate from intering my linux telecommunicate server.a individual crapper recieve 90 messages a period from uncharted recipients.