A couple of friends are receiving dodgy e mails from my address, however I am not sending them.
That suggests that those emails are being "spoofed". In other words the sender is making then appear to come from your email address but is actually sending them from another email account that they control.
My female friend blocked the sender and didn't receive anything for a while but it has started again.
That pretty much confirms that despite appearances those dodgy emails are not coming from your email address but they are simply spoofing your email address. If the emails come from your email address then when your friend blocked the sender of those dodgy emails they would also have blocked genuine emails from you.
If the block originally stopped the dodgy emails being received but no longer does, then it means the spammer/scammer was originally sending from one email account and has now changed to using a different account. Spammers and scammers regularly change the email account they use to send their dodgy emails simply to avoid being blocked.
Spoofed emails have been common since the earliest days of email. There has always been a basic weakness with email in general in that the email address in the From: and Sender: fields in an email header does not have to be the email address that the email actually comes from.
A spammer can send simply forge the From: and Sender: details in an email to make it appear that it is coming from your VM email account, (or anyone-else's account come to that) and they do not need access to your VM email account or the VM email servers to do that.
Therefore, once a spammer knows your email address they can continue to spoof emails so they appear to come from your address even if the email account itself no longer exists.
Scammers spoof email addresses to make the recipient think the email is coming from a trusted source, (your bank for example).
Spammers often do it to simply hide their own email address and ensure that any rejection or non delivery messages that get generated by their spoofed emails are sent to your email address not theirs!
Here's a good overview of what spoofing is and how it's done https://www.proofpoint.com/uk/threat-reference/email-spoofing
Is there anyway I can prevent this happening?
If the emails are being spoofed, there is nothing that you or VM can do to stop it. Even deleting your VM email account will not stop them.
However, it would be wise to change your email password just in case your email account has been compromised.
I'm a Very Insightful Person, I'm here to share knowledge, I don't work for Virgin Media. Learn more
Have I helped? Click Mark as Helpful Answer or use Kudos to say thanks