BleepingComputer.com: Has my email address been hijacked?

Greetings all

I use Thunderbird for my work email - my employer and therefore email server is based in Australia (I'm in the UK) and it all works fine.
However several times in the past few weeks I've had email bounces listing a stack of addresses I didn't send emails to. All points to spoofing
but the strange thing is that the subject line does match an email I DID send out shortly before...

Have run AVG and Kaspersky and no viruses found on my laptop at all. Could it be something at the server end??

I'm at a loss to know what's going on

When dealing with work - related emails, your best course of action would be to notify your employer about what is happening. They would then investigate on their end & see if anything is amiss.