Re: Help wanted.
Possible solutions in no particular order?
The answer by PatsCG might work if you are able to contact them and get a response?
Are you in a position to check if everybody on your contacts list is receiving your mail messages?
You either typed the address in wrong or the person you mailed no longer has a mail account at that address
Mailer Daemon is generally a way of telling you that the email you sent either doesn't exist, is wrong or cant accept emails.
I would check the email addresses you are sending to and make sure they are correct.
The mailer-daemon message is actually from your own email server, not from the intended recipient.
It is informing you that the message is undeliverable.
It could be that the intended recipient's email inbox is full so the message is returned.
You might have some success if you are able to use the Settings/Filters and create a filter specific to that message set to auto-delete.
Another option is to try a system restore and take it back to a time when everything was working ?
You might also have a Trojan on board?
Most virus killers should be able to identify them
Do you have Spybot Search & Destroy and Spyware Doctor as they also help to remove Malware?
Another way is to set up another gmail address and gradually migrate everything over to that one