Firstly, I do not know if this is an ISP problem or not, but this seems as good a place as any to start.

I dont send a lot of emails but since yesterday afternoon (maybe earlier) I have been unable to email my parents who have a netsmart email account.

I have also sent an email to my gmail account ( as a test) and that has not appeared either.

To make matters complicated, one email (out of 7 or 8) did get through to Dad.

The rest have come back undeliverable quoting spamhaus or sorbs and with a link I'm not sure I should click on.

I didnt get an undeliverable report for the gmail message.

I think emails to some other addresses might be working, but only because I have not got an undeliverable report back for those, the recipients have not replied so I dont know for sure.

 My Dad has spoken to his ISP who have firmly batted the ball into Vodafone's court, no surprises there.

Any ideas as to what is happening?